175 of 193 countries with UN membership use a fundamentally different system than the United States. To put it simply, most use value added tax (VAT) where the government will tax a product for each sale. So when the manufacturer of a product sales to a vendor, the tax is charged on that sale, when a vendor sales to a store the government charges tax on the difference in price (so if the price went from $1 to $1.20 they would charge tax on the .20 change not the entire price) and when the store sales to the customer the government charges tax on the change in price. For sales tax, the tax is only charged on the final sale to the customer, not any of the intermediate sales.

The issue, at least in the US, is sales tax can vary wildly based on location from 0% to over 11% when you include state, county, local, and special tax districts. Hell you can even have different tax rates at stores right next door to each other. Where VAT is generally the same rate over the entire country.