From US Customs site
Tobacco Products: You may include up to 100 cigars and up to 200 cigarettes in your duty-free exemption. If you bring back more than these amounts, you will have to pay duty on them, even if you have not gone over your duty-free exemption. You may also have to pay state or local taxes on tobacco products.
This tobacco exemption is available to each person. Tobacco products of Cuban origin, however, are prohibited unless you actually acquired them in Cuba and are returning either directly or indirectly from that country on licensed travel. You may not, for example, bring in Cuban cigars purchased in Canada.
