Rounding a floating point value to a certain precision

For my work, I needed to round a floating point value (double in C#) to a precision of 0.05. Unfortunately, Math.Round only lets you round a value to the nearest decimal. That means you can only round to 0.1, 0.01, 0.001, ... To round your values to 0.05, or 0.25, or whatever, I created the following function:
In C#:

public static double Round(double x, int numerator, int denominator)
{ // returns the number nearest x, with a precision of numerator/denominator
 // example: Round(12.1436, 5, 100) will round x to 12.15 (precision = 5/100 = 0.05)
 long y = (long)Math.Floor(x * denominator + (double)numerator / 2.0);
 return (double)(y - y % numerator)/(double)denominator;
}

In Euphoria:

global function Round(atom x, integer numerator, integer denominator)
 -- returns the number nearest x, with a precision of numerator/denominator
 -- example: Round(12.1436, 5, 100) will round x to 12.15 (precision = 5/100 = 0.05)
 integer y
 y = floor(x * denominator + numerator / 2.0)
 return (y - remainder(y, numerator)) / denominator
end function

Win4Eu: first overview of code

On the Win4Eu-forum of UBoard, I posted an overview of what I have coded so far.