double dou = 1.255;

//这种是错误的

double dou_result = Math.Round(dou, 2); //结果: 1.25

dou_result = Math.Round(dou, 2, MidpointRounding.AwayFromZero); //结果: 1.25

//这种是正确的，如//996.68225，保留4位小数

decimal dec_result = Math.Round(Convert.ToDecimal(dou), 2,MidpointRounding.AwayFromZero);//结果:1.26

double true_double = Convert.ToDouble(dec_result); //结果:1.26