Bitcoin didn't has a tax ,because although the government take tax from bitcoin but bitcoin can used anonimously , so the government can't trace history of bitcoin .so they can't do anything. I think we do not have to worry.
i am not sure whether this statement is completely true,bitcoin is an open source ledger,hope you have heard the case about Ross William Ulbricht andAtrem Vaulin they were not that anonimous and were involved in illegal activities but they are caught and all of their coins are Confiscated
