If you force everyone to put their money into a bank, then anyone who pays their taxes already has their $900 in assets accounted for and don't need to pay more taxes. If you have $10,000 in cash you need to deposit into a bank and no documentation for it... you'll have a bad time.
There is no musical chairs, since the money flows upwards. If you are honest, you should not get hit by any additional taxes.
This is the reason why currently most of India supports the move of discontinuing the old currency and replacing it. Unless you take in a large amount over your taxed salary as untaxed bribes, it doesn't affect the amount of money you have.