C#中的Math.Round使用的"四舍五入"法
C#中的Math.Round()并不是使用的"四舍五入"法。其实在VB、VBScript、C#、J#、T-SQL中Round函数都是采用Banker's rounding（银行家算法），即：四舍六入五取偶。事实上这也是IEEE的规范，因此所有符合IEEE标准的语言都应该采用这样的算法。
.NET 2.0 开始，Math.Round 方法提供了一个枚举选项 MidpointRounding.AwayFromZero 可以用来实现传统意义上的"四舍五入"。即： Math.Round(4.5, MidpointRounding.AwayFromZero) = 5。
Round(Decimal)
Round(Double)
Round(Decimal, Int32)
Round(Decimal, MidpointRounding)
Round(Double, Int32)
Round(Double, MidpointRounding)
Round(Decimal, Int32, MidpointRounding)
Round(Double, Int32, MidpointRounding)
如：
Math.Round(0.4) //result:0
Math.Round(0.6) //result:1
Math.Round(0.5) //result:0
Math.Round(1.5) //result:2
Math.Round(2.5) //result:2
Math.Round(3.5) //result:4
Math.Round(4.5) //result:4
Math.Round(5.5) //result:6
Math.Round(6.5) //result:6
Math.Round(7.5) //result:8
Math.Round(8.5) //result:8
Math.Round(9.5) //result:10
使用MidpointRounding.AwayFromZero重载后对比：
Math.Round(0.4, MidpointRounding.AwayFromZero); // result:0
Math.Round(0.6, MidpointRounding.AwayFromZero); // result:1
Math.Round(0.5, MidpointRounding.AwayFromZero); // result:1
Math.Round(1.5, MidpointRounding.AwayFromZero); // result:2
Math.Round(2.5, MidpointRounding.AwayFromZero); // result:3
Math.Round(3.5, MidpointRounding.AwayFromZero); // result:4
Math.Round(4.5, MidpointRounding.AwayFromZero); // result:5
Math.Round(5.5, MidpointRounding.AwayFromZero); // result:6
Math.Round(6.5, MidpointRounding.AwayFromZero); // result:7
Math.Round(7.5, MidpointRounding.AwayFromZero); // result:8
Math.Round(8.5, MidpointRounding.AwayFromZero); // result:9
Math.Round(9.5, MidpointRounding.AwayFromZero); // result:10