Bitcoin itself has no tax or it will be hard for the government to put tax on a decentralised currencies such as bitcoins and altcoins because it will be hard for them to trace the identity of the bitcoin holders but the moment we converted our bitcoins into fiat then the taxes occur. Like for example i converted my bitcoin into cash from my ewallet and deposited it directly into my bank accounts. Then the government have it controlled already and from there they can taxes on it.