我的解决方案将输入视为字符串，并使用n位数字的“数学舍入”算法：取n位数字，如果数字n+1等于或大于5，则加1。它还允许指定负数，例如，将123.45舍入为-1的数字为120。它也适用于科学符号（例如1.2e-3）。我没有测量它的速度，我认为这不是最好的表现。

function safeRound( numInput, numPrecision ) {
    const strNumber = numInput.toString().replace( 'E', 'e' );
    const bSign = '+-'.indexOf( strNumber[ 0 ] ) !== -1;
    const strSign = bSign  ?  strNumber[ 0 ]  :  '';
    const numSign = strSign !== '-'  ?  +1  :  -1;
    const ixExponent = ( ixFound => ixFound !== -1  ?  ixFound  :  strNumber.length )( strNumber.indexOf( 'e' ) );
    const strExponent = strNumber.substr( ixExponent + 1 );
    const numExponent = ixExponent !== strNumber.length  ?  Number.parseInt( strExponent )  :  0;
    const ixDecimal = ( ixFound => ixFound !== -1  ?  ixFound  :  ixExponent )( strNumber.indexOf( '.' ) );
    const strInteger = strNumber.substring( !bSign  ?  0  :  1, ixDecimal );
    const strFraction = strNumber.substring( ixDecimal + 1, ixExponent );
    
    const numPrecisionAdjusted = numPrecision + numExponent;
    const strIntegerKeep = strInteger.substring( 0, strInteger.length + Math.min( 0, numPrecisionAdjusted ) ) + '0'.repeat( -Math.min( 0, numPrecisionAdjusted ) );
    const strFractionKeep = strFraction.substring( 0, Math.max( 0, numPrecisionAdjusted ) );
    const strRoundedDown = strSign + ( strIntegerKeep === ''  ?  '0'  :  strIntegerKeep ) + ( strFractionKeep === ''  ?  ''  :  '.' + strFractionKeep ) + ( strExponent === ''  ?  ''  :  'e' + strExponent );
    
    const chRoundUp = 0 <= numPrecisionAdjusted  ?  strFraction.substr( numPrecisionAdjusted, 1 )  :  ( '0' + strInteger ).substr( numPrecisionAdjusted, 1 );
    const bRoundUp = '5' <= chRoundUp && chRoundUp <= '9';
    const numRoundUp = bRoundUp  ?  numSign * Math.pow( 10, -numPrecision )  :  0;
    
    return Number.parseFloat( strRoundedDown ) + numRoundUp;
}

function safeRoundTest( numInput, numPrecision, strExpected ) {
    const strActual = safeRound( numInput, numPrecision ).toString();
    const bPassed = strActual === strExpected;
    console.log( 'numInput', numInput, 'numPrecision', numPrecision, 'strExpected', strExpected, 'strActual', strActual, 'bPassed', bPassed );
    return bPassed  ?  0  :  1;
}

function safeRoundTests() {
    let numFailed = 0;
    numFailed += safeRoundTest( 0, 0, '0' );
    numFailed += safeRoundTest( '0', 0, '0' );
    numFailed += safeRoundTest( '0.1', 0, '0' );
    numFailed += safeRoundTest( '+0.1', 0, '0' );
    numFailed += safeRoundTest( '-0.1', 0, '0' );
    numFailed += safeRoundTest( '0.1', 1, '0.1' );
    numFailed += safeRoundTest( '+0.1', 1, '0.1' );
    numFailed += safeRoundTest( '-0.1', 1, '-0.1' );
    numFailed += safeRoundTest( '0.9', 0, '1' );
    numFailed += safeRoundTest( '+0.9', 0, '1' );
    numFailed += safeRoundTest( '-0.9', 0, '-1' );
    numFailed += safeRoundTest( '0.9', 1, '0.9' );
    numFailed += safeRoundTest( '+0.9', 1, '0.9' );
    numFailed += safeRoundTest( '-0.9', 1, '-0.9' );
    numFailed += safeRoundTest( '0.5', 0, '1' );
    numFailed += safeRoundTest( '+0.5', 0, '1' );
    numFailed += safeRoundTest( '-0.5', 0, '-1' );
    numFailed += safeRoundTest( '0.4999', 0, '0' );
    numFailed += safeRoundTest( '+0.4999', 0, '0' );
    numFailed += safeRoundTest( '-0.4999', 0, '0' );
    numFailed += safeRoundTest( '1.005', 2, '1.01' );
    numFailed += safeRoundTest( '1.00499999999', 2, '1' );
    numFailed += safeRoundTest( '012.3456', -4, '0' );
    numFailed += safeRoundTest( '012.3456', -3, '0' );
    numFailed += safeRoundTest( '012.3456', -2, '0' );
    numFailed += safeRoundTest( '012.3456', -1, '10' );
    numFailed += safeRoundTest( '012.3456', 0, '12' );
    numFailed += safeRoundTest( '012.3456', 1, '12.3' );
    numFailed += safeRoundTest( '012.3456', 2, '12.35' );
    numFailed += safeRoundTest( '012.3456', 3, '12.346' );
    numFailed += safeRoundTest( '012.3456', 4, '12.3456' );
    numFailed += safeRoundTest( '012.3456', 5, '12.3456' );
    numFailed += safeRoundTest( '12.', 0, '12' );
    numFailed += safeRoundTest( '.12', 2, '0.12' );
    numFailed += safeRoundTest( '0e0', 0, '0' );
    numFailed += safeRoundTest( '1.2e3', 0, '1200' );
    numFailed += safeRoundTest( '1.2e+3', 0, '1200' );
    numFailed += safeRoundTest( '1.2e-3', 0, '0' );
    numFailed += safeRoundTest( '1.2e-3', 3, '0.001' );
    numFailed += safeRoundTest( '1.2e-3', 4, '0.0012' );
    numFailed += safeRoundTest( '1.2e-3', 5, '0.0012' );
    numFailed += safeRoundTest( '+12.', 0, '12' );
    numFailed += safeRoundTest( '+.12', 2, '0.12' );
    numFailed += safeRoundTest( '+0e0', 0, '0' );
    numFailed += safeRoundTest( '+1.2e3', 0, '1200' );
    numFailed += safeRoundTest( '+1.2e+3', 0, '1200' );
    numFailed += safeRoundTest( '+1.2e-3', 0, '0' );
    numFailed += safeRoundTest( '+1.2e-3', 3, '0.001' );
    numFailed += safeRoundTest( '+1.2e-3', 4, '0.0012' );
    numFailed += safeRoundTest( '+1.2e-3', 5, '0.0012' );
    numFailed += safeRoundTest( '-12.', 0, '-12' );
    numFailed += safeRoundTest( '-.12', 2, '-0.12' );
    numFailed += safeRoundTest( '-0e0', 0, '0' );
    numFailed += safeRoundTest( '-1.2e3', 0, '-1200' );
    numFailed += safeRoundTest( '-1.2e+3', 0, '-1200' );
    numFailed += safeRoundTest( '-1.2e-3', 0, '0' );
    numFailed += safeRoundTest( '-1.2e-3', 3, '-0.001' );
    numFailed += safeRoundTest( '-1.2e-3', 4, '-0.0012' );
    numFailed += safeRoundTest( '-1.2e-3', 5, '-0.0012' );
    numFailed += safeRoundTest( '9876.543e210', 0, '9.876543e+213' );
    numFailed += safeRoundTest( '9876.543e210', -210, '9.877e+213' );
    numFailed += safeRoundTest( '9876.543e210', -209, '9.8765e+213' );
    numFailed += safeRoundTest( '9876.543e+210', 0, '9.876543e+213' );
    numFailed += safeRoundTest( '9876.543e+210', -210, '9.877e+213' );
    numFailed += safeRoundTest( '9876.543e+210', -209, '9.8765e+213' );
    numFailed += safeRoundTest( '9876.543e-210', 213, '9.876543e-207' );
    numFailed += safeRoundTest( '9876.543e-210', 210, '9.877e-207' );
    numFailed += safeRoundTest( '9876.543e-210', 211, '9.8765e-207' );
    console.log( 'numFailed', numFailed );
}

safeRoundTests();

parseFloat（“1.555”）.toFixed（2）；//返回1.55而不是1.56。

1.55是绝对正确的结果，因为在计算机中不存在1.555的精确表示。如果读数为1.555，则四舍五入至最接近的值=1.55499999999999994（64位浮点）。将这个数字四舍五入到Fixed（2）得到1.55。

如果输入为1.55499999999999，则此处提供的所有其他功能都会给出故障结果。

解决方案：在扫描前加上数字“5”，将数字舍入（更准确地说，从0开始舍入）。仅当数字真的是浮点（有小数点）时才执行此操作。

parseFloat("1.555"+"5").toFixed(2); // Returns 1.56

所有浏览器和精度的通用答案：

function round(num, places) {
    if(!places) {
        return Math.round(num);
    }

    var val = Math.pow(10, places);
    return Math.round(num * val) / val;
}

round(num, 2);

从现有的答案中，我找到了另一个似乎很有效的解决方案，它也可以发送字符串，并消除尾随零。

function roundToDecimal(string, decimals) {
    return parseFloat(parseFloat(string).toFixed(decimals));
}

如果你派一些公牛来，那就不算什么了。。就像“阿帕”一样。或者它可能会抛出一个错误，我认为这是正确的方法。无论如何，隐藏应该修复的错误（通过调用函数）是不好的。

这可能会帮助您：

var result = Math.round(input*100)/100;

有关更多信息，您可以查看Math.round（num）vs num.toFixed（0）和浏览器不一致性

最简单的方法：

+num.to固定（2）

它将其转换为字符串，然后再转换为整数/浮点。