How to Truncate decimal values in C#

Question

I am trying to truncate the values (without rounding) according to the number of decimals passed per parameter, but the Math.Truncate function does not have this feature... Is there any way I can do this?

public static decimal TruncarValor(decimal valor, int casasDecimais)
{
   return Math.Truncate(valor, casasDecimais????????);
}

Hug to all!