From MSDN (
http://msdn.microsoft.com/en-us/library/75ks3aby.aspx[
^]):
Notes to Callers
Because of the loss of precision that can result from representing decimal values as floating-point numbers or performing arithmetic operations on floating-point values, in some cases the Round(Double, Int32) method may not appear to round midpoint values to the nearest even value in the digits decimal position. This is illustrated in the following example, where 2.135 is rounded to 2.13 instead of 2.14. This occurs because internally the method multiplies value by 10 * digits, and the multiplication operation in this case suffers from a loss of precision.