How to round decimal value up to nearest 0.05 value?

Use this:

Math.Round(mydecimal / 0.05m, 0) * 0.05m;

The same logic can be used in T-SQL:

ROUND(@mydecimal / 0.05, 0) * 0.05

I prefer this approach to the selected answer simply because you can directly see the precision used.

How about:

Math.Ceiling(myValue * 20) / 20