Math.Round() problem - inconsistent result

The problem I am having is that when I use the following Math.Round() code, it rounds up to the nearest whole number but that is not consistent with different input values.

double result = 0;double amount = 20.955;
result = Math.Round(amount, 2);Console.WriteLine(result);

Result: 20.96
if amount = 19.955 then the result is 19.95
amountresult
7.955		7.96
8.955		8.96
12.955		12.96
15.955		15.96
16.955		16.95
17.955		17.95
18.955		18.95
20.955		20.96
27.955		27.96
If you can closely observe the above values then you can find some inconsistency when rounding using Math.Round() method.
Could someone let me know the algorithm it uses to compute the rounding?
Thanks,
Kishore