A "dime" is a denomination of coin in the U.S., Canada, and a few other countries. It's worth 10 cents, or 1/10 of a dollar.
The unusual name is left over from a proposed currency system that was...
Some one would sponsor the person marching and give them a dime for every mile they walked or something similar.The march of dimes in a charity that helps improve health of babies.
Technically the coins are supposed to be called Liberty dimes and the winged Liberty cap worn by Miss Liberty is supposed to symbolize freedom. But the design looks so much like the winged helmet...