Back then buck skin was 1$ so a "buck" is classified as a dollar

*sits in a polished black leather chair* "Their is actually a history to the name. Back then as you know everything was extremely low in prices compared to today's worth for food, etc. But deer skin or "buck skin" was usually worth a dollar, now this was a nice wage of money especially due to the fact deer populations were so high and forests existed thickly within most of the U.S. So the name in the end, one "buck" equaled a legitimate dollar pay back in the day decades to a hundred or two years ago."

Because bucks sounds cooler.