To be honest, when it happens, there will be no FIAT money anymore. The government currency system will totally collapse and there will be a revolution of Cryptocurrency which is leaded by Bitcoin users. There will be no tax in the world and it will be much better when there is only one currency in the world: Bitcoin
That is just an imagination but reality would be totally different from that, as no government would let that happen as in that way they would lose control on the country or on the economic system of it which is something no government would want, and if that happens governments would go bankrupt i guess if there will be no tax at all.