Math.Round() 银行家舍入

四舍五入VS银行家舍入 (四舍六入五取偶)

银行家舍入的规律：四舍六入五考虑，五后非零就进一，五后为零看奇偶，五前为偶应舍去，五前为奇要进一
Math.Round() ——银行家舍入
Math.Round(4.5, MidpointRounding.AwayFromZero) = 5 ——实现四舍五入
Math.Round(4.5111, 2,MidpointRounding.ToEven) ——保留2位小数

MidpointRounding.AwayFromZero：When a number is halfway between two others, it is rounded toward the nearest number that is away from zero

MidpointRounding.ToEven：When a number is halfway between two others, it is rounded toward the nearest even number.