Somebody's confused here. The term "voyage to nowhere" means exactly that ... a cruise that sails the seas for a period of time without stopping at a foreign port and then returns to the originating port. Since you have not visited a foreign place, you have not earned entitlement to duty-free exemptions. No clearance by U.S. Customs is necessary. If the vessel's shops sell goods during that voyage, they are either of domestic (U.S.) origin or duty has already been paid by the vendor. Liquors and tobacco products, whether of U.S. or foreign origin, are not duty- or tax-free under any circumstances if the ship doesn't touch a foreign port. So IF you are permitted to buy these items, you can be sure that duties and internal revenue taxes are included in the price you pay. There are no great "bargain" purchases on this type of cruise, but that doesn't mean that you can't have a great time. Happy "nowhere" cruising!
I guess a better question would have been: What's the purpose of a "cruise to nowhere"? Is it a shake down? AND where do they sail out of and how do you find out about them? I never see them advertised. Please excuse the appearance of confusion.
There is a 2 day Cruise to Nowhere out of Norfolk VA on the Victory. Usually one in June and one in October. Its a cheap way to see if you like cruising or to cruise when your funds and/or vacation time are low. The one out of Norfolk starts at $159. I found it on Expedia - Carnival didnt list it.