Well, first things first, You should pay your taxes and otherwise be a law abiding citizen.
So with that being said the ideal is crypto should be free from all form of govt regulations so if You have money in bitcoin. No one knows that you have money in bitcoin, and no one tries to tax the money that is in bitcoin.

But in reality you either live in a country with competent tax authorities, or one with incompetent ones. If your country has incompetent tax authorities, then there are a dozen other easier ways to hide your money. If you have one with competent tax authorities, they can follow the money and find it although anonymous protocol such as Zerocoin and the rest can give them tough time.