There is no selling price "5. Tax deducted from selling price". This law only applies to trades done with money.
The key to the law is here "and pays, or becomes liable to pay, the tax imposed under this section". For a person to become liable to 'pay', there needs to be money involved. No money, no liability.
Yep, but BTC is still traded for money, not potatoes or cabbages. So tax will be eventually applied, soon or later.