A tax based on the cost of the item purchased and collected directly from the buyer WordNet 3.0 & Open English WordNet

A sales tax is a tax paid to a governing body for the sales of certain goods and services. Wikipedia

A tax imposed as a percentage of the selling price of goods or services, payable by the customer and transmitted by the seller to the taxing authority; a sales tax. Wiktionary

A local or state tax imposed as a percentage of the selling price of goods or services payable by the customer. The tax is not recognized as the seller's earnings; the seller only collects the tax and transmits the same to local or state authorities. Wiktionary

Tax. Wiktionary (translation)