It’s just the name for sales tax. Why is there a tax on sales, isn’t a sale a discount? Then is the sales tax negative because it’s the tax on the difference between the full price and the discounted price? You’d probably end up with a refund for buying the thing, unless your state has no sales tax.

Sales tax is actually very different beacuse it is usually either cumulative and added to each part of the chain, or only the last one; whereas VAT is deducted in all but the last part of the chain.