It is illegal to bring Cuban cigars into the U.S.
If you do a search on Cruisemates some people have written about how they got away with importing them, but you face stiff penalties if you are caught. Like Nanatravel says, it is up to you. Personally I don't think it's worth the risk.
Dominican cigars are excellent quality and legal to import. Ask your brother if he would mind having some of those instead.