Numbers and dates only gain a "format" when you convert them to a string, so the answer to your question is that you can't store your float in a certain format. Keep it as float and when you want to show it convert it to a string of the required format;
float f = 10F;
System.Diagnostics.Debug.WriteLine(f.ToString("0.00"));
f = 1.123F;
System.Diagnostics.Debug.WriteLine(f.ToString("0.00"));