Since each state operates independent of the Federal government for the most part, they must find their own ways to generate income in order to provide goods, services, and a governing body for its people. The implementation of sales taxes is one way that states are able to meet their budgets. Of course, those on the receiving end of the deal—the consumers—do not see it as a fair trade, especially since most states also charge a state income tax as well.
Which tax is fairer to the low income? That depends where you live. In states that have exemptions for food, most clothing, and prescriptions, the lower income will benefit because the items that must have will not be subject to sales taxes. On the other hand, in states that charge sales taxes on nearly everything you buy, the exchange is not as equitable, especially if they also charge sales taxes on unprepared food.