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.
as had been spoken by so many people repeatedly and very often,bitcoin is not fully anonymous,each transaction you have made can be traced by using blockchain explorer, therefore it's usually called pseudo-anonymous,and if bitcoin can't tax you directly,they can tax you while buying stuff through the merchants