I count 15 separate ways...
20 dimes
15 dimes, 1 half dollar
15 dimes, 2 quarter
10 dimes, 2 half dollars
10 dimes, 4 quarters
10 dimes, 1 half dollar, 2 quarters
5 dimes, 3 half dollars
5 dimes, 2 half dollars, 2 quarters
5 dimes, 1 half dollar, 4 quarters
5 dimes, 6 quarters
8 quarters
4 half dollars
6 quarters, 1 half dollar
4 quarters, 2 half dollars
2 quarters, 3 half dollars
That's 15