The Federal Government has ALWAYS had and used a sales tax. In the constitution it is called a “excise tax”. Today it is applied to alcohol, transportation fuels, tobacco products, vaccines, land-line telephone usage, firearms and ammo and other products and services.
Nothing stops it from being expanded to other products by the legislature.
The federal excise taxes are not added to the bill, they are incorporated in the sales price, but AFAIK, nothing in the Constitution’s definition of taxes stops them from being tallied at the point-of-sale as a separate item, just like the state sales taxes are.