Kick Out The Old Tax Books!

The whole world agrees that the U.S. has the most complex and useless tax systems in the world. Which makes since beings that the book is five thousand pages long, and no one person really understands how the system works. We propose that the old tax system should be replaced with a national sales tax of something around 10%-15%.
According to a 2012 census the GDP of the U.S. was 15.68 Trillion, at 313.9 million U.S. citizens, but with a National Sales Tax of just 15%, if all 313.9 million U.S. citizens were to make just one purchase of $620 USD each, or 31 sub-sequent $20 USD purchases each, the U.S. would have a GDP of $29,192,700,000 USD; those numbers are just with U.S. citizens though. The actual GDP would be much greater, as a National Sales Tax would be paid by tourists as well.