Have yoi tried
Decimal.Truncate(Decimal) Method (System) | Microsoft Docs[
^] - that is what it is designed to do...
decimal d = 3.31M;
Console.WriteLine("{0}, {1}, {1:0.00}", d, decimal.Truncate(d));
Dim d As Decimal = 3.31D
Console.WriteLine("{0}, {1}, {1:0.00}", d, Decimal.Truncate(d))