round.js

function round(value, precision, mode) {
    var m, f, isHalf, sgn;
    precision |= 0;
    m = Math.pow(10, precision);
    value *= m;
    sgn = (value > 0) | -(value < 0);
    isHalf = value % 1 === 0.5 * sgn;
    f = Math.floor(value);

    if ( isHalf ) {
        switch (mode) {
            case 'PHP_ROUND_HALF_DOWN':
                // rounds .5 toward zero
                value = f + (sgn < 0);
            break;
            case 'PHP_ROUND_HALF_EVEN':
                // rouds .5 towards the next even integer
                value = f + (f % 2 * sgn);
            break;
            case 'PHP_ROUND_HALF_ODD':
                // rounds .5 towards the next odd integer
                value = f + !(f % 2);
            break;
            default:
                // rounds .5 away from zero
                value = f + (sgn > 0);
        }
    }

    return ( isHalf ? value : Math.round(value) ) / m;
}