Can pay tax when the respected country accepts bitcoin. If the income is high and crossed the threshold government has set to the individual then yes please pay the tax required though it does not ask for it as you are bond to pay it. Many countries are yet to adapt bitcoin and other crypto currencies. In such cases,  though one is bound to pay,  it can be omitted as long as the transaction is not tracked. But be aware of the tax implementation when one crosses the limit.