More and more countries, like Chile or India, are trying to tax their citizen for the crypto they hold.
Please don't pay taxes on your coins.
You really don't need it, unless you are totally ignorant.
It's simple: they cannot prove you have the coins on your PC/phone , so you don't have nothing to pay taxes on, as far as they know.
It's just their attempt to trick the ignorants that don't know about that 
Even if they look for your wallet on your PC/phone ,
your wallet data is not accessible to them because it's encrypted with password ( uhm.... have you set the password protection on your wallet... right?

).
Tax is charged on an exchange transaction when you want to exchange your coins for real money. This is done automatically when you make a currency transaction.