js计算四舍五入的值（函数封装）

/**

• 将数值四舍五入(保留2位小数)后格式化成金额形式
• @param num 数值(Number或者String)
• @return 金额格式的字符串,如'1,234,567.45'
• @type String
  */

function formatCurrency(num) {
    num = num.toString().replace(/\$|\,/g,'');
    if(isNaN(num))
        num = "0";
    sign = (num == (num = Math.abs(num)));
    num = Math.floor(num*100+0.50000000001);
    cents = num%100;
    num = Math.floor(num/100).toString();
    if(cents<10)
    cents = "0" + cents;
    for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++)
    num = num.substring(0,num.length-(4*i+3))+','+
    num.substring(num.length-(4*i+3));
    return (((sign)?'':'-') + num + '.' + cents);
}