A federal sales tax would only achieve the same thing that the current income tax does.
While it sounds right on the outside, a tax such as this is really no better or different than an income tax. The income tax is figured on a progressive scale that has people who earn more paying a higher percentage than those earning less. Since richer people have more money, they obviously buy more stuff, and would, once again, pay more in taxes. Therefore, a tax like this would achieve nothing and look very underhanded and bad on our government's part.