AS3：将数字舍入到特定的位数，而不使用toFix方法？

Question

我收到错误＃1008，但为了让事情有效，我需要添加什么？

private function rounding()
{
    var originalNumber:Number = 2.97849382;
    var rounded:Number = 2;

    //just calculating by ones, which gives 2.98. if by two you would get 2.9785
    trace("The original number was " +originalNumber+ " Rounded to " +rounded+ " digits, the number is " 
        +round(2.97849382, 1));
    }

private function round(num:Number, precision:int):Number//using perameters to get info that is passed to them
{
    var decimalPlaces:Number = Math.pow(100, precision);//change the number here to change the decimal place
    return Math.round(decimalPlaces * num) / decimalPlaces;//calculating the answer, and returning the answer to the problem        
}