Problem in Round Function C#

Question

hello every one,

well i have very big problem in Round Function when i m putting 3 digit number in text box than its not give me round function but if i m putting 2 digit number in text box than its convert into round function i dont know what wrong with that..............

double num = 100.5;            num = Math.Round(num);//100

double num1 = 100.51;            num = Math.Round(num);//101

but i want 100.5 as 101..........

hope u understand my problem.

thanks in Advance