Not sure about where you live, but in my state, I walk up to the counter, pays my money and takes my choice (of what's available) when it comes to buying ammo. No paperwork. That 11% is get off my frigging back money.
That isn't the case with a can. You get to register your can (and be a gun owner in the file).
I live in the good old U.S. or A. and pay the Pittman-Robertson tax on each gun and cartridge that I buy. I am aware of the tax. Apparently you are not.
Pittman-Robertson Federal Aid in Wildlife Restoration Act was established in 1937 for federal aid in wildlife Restoration Act. It in itself is a good tax used for a good purpose, but hidden from view to customers like you. It is charged directly to the manufacturers of firearms and ammunition and simply passed on through the retail distribution system to you. You pay many such hidden taxes, some of which are not well intended. Look at your phone bill sometime to see how many partially hidden taxes that you pay.