The usual U.S. customs rules and allowances don't apply to travel in Cuba. The embargo forbids bringing back Cuban goods such as cigars and rum. There are exceptions for art and educational materials, so paintings, music CDs and handicrafts are OK.
When you get back to the states, Customs may inspect your bags . If you say "Nothing to declare" and they find cigars, you could be in big trouble. To me, it isn't worth the risk.
Customs allow a lot
On your departure, you're allowed to take as many bottles of Rhum and as many Cigars as you want, as long as they're official ones and not from the black market. But don't forget ! Your country might not accept unlimited importing.