The interesting thing many don't know is that taxes are actually unnecessary, as the Fed and policymakers have said for many years. Taxes are now used as an instrument of social control. For ex, want people to drive less? Raise the tax on gas. Want people to stop smoking? Guess how.
Financing the federal government by simply giving the Fed sufficient T-Bonds/bills in exchange for cash (actually computer entries) is far easier than collecting a bizarre and obsolete tax.