Rounding to the nearest 1000 in C#

Working on that demo app, this came up - I wanted a number rounded to the nearest 1000. This is easy enough in Excel - the ROUND function takes negative values, so that =ROUND(2009,-3) will give you 2000. The Math.Round function in System.dll doesn't offer this functionality however - you have to implement that yourself. Here's an example of one way to do this:

using System;

static class Program

{

    static void Main(string[] args)

    {

        double d = (double)new Random().Next();

        // round to the nearest 1000

        Console.WriteLine("{0} rounded to the nearest thousand is {1}", d, Round(d, -3));

        // round to the nearest 100 etc

        Console.WriteLine("{0} rounded to the nearest hundred is {1}", d, Round(d, -2));

    }

    static double Round(double value, int digits)

    {

        if ((digits < -15) || (digits > 15))

            throw new ArgumentOutOfRangeException("digits", "Rounding digits must be between -15 and 15, inclusive.");

        if (digits >= 0)

            return Math.Round(value, digits);

        double n = Math.Pow(10, -digits);

        return Math.Round(value / n, 0) * n;

    }

    static decimal Round(decimal d, int decimals)

    {

        if ((decimals < -28) || (decimals > 28))

            throw new ArgumentOutOfRangeException("decimals", "Rounding decimals must be between -28 and 28, inclusive.");

        if (decimals >= 0)

            return decimal.Round(d, decimals);

        decimal n = (decimal)Math.Pow(10, -decimals);

        return decimal.Round(d / n, 0) * n;

    }

}