According to the documentation, the decimal.Round method uses a round-to-even algorithm which is not common for most applications. So I always end up writing a custom functi
The other answers with reasons why the Banker's algorithm (aka round half to even) is a good choice are quite correct. It does not suffer from negative or positive bias as much as the round half away from zero method over most reasonable distributions.
But the question was why .NET use Banker's actual rounding as default - and the answer is that Microsoft has followed the IEEE 754 standard. This is also mentioned in MSDN for Math.Round under Remarks.
Also note that .NET supports the alternative method specified by IEEE by providing the MidpointRounding
enumeration. They could of course have provided more alternatives to solving ties, but they choose to just fulfill the IEEE standard.