using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        var amount = "47.110815";

        //2 digits

        var decimalValue = Decimal.Parse(amount.GetDecimalStringWithoutRounding(2), CultureInfo.InvariantCulture);

        Console.WriteLine(decimalValue);

        //3 digits

        decimalValue = Decimal.Parse(amount.GetDecimalStringWithoutRounding(3), CultureInfo.InvariantCulture);

        Console.WriteLine(decimalValue);

    }

}

​

public static class Extension

{

    public static string GetDecimalStringWithoutRounding(this string decimalValue, int numberOfDigits)

    {

        int getIndexOfDot = decimalValue.IndexOf("."); 

        return decimalValue.Remove((numberOfDigits+1)+2);

    }

}