Taxes are usually at the national or local level (sometimes limited to several international contexts, such as VAT EU). Like laws vary from country to country.
There is no "property tax" on the Bitcoin that I realized in any law.
Anyway in most legislates when you sell Bitcoin (and Altcoin) at a higher price than you buy, applying some taxation, usually the same taxation in the country is applied to financial / capital profits. If you sell something in Bitcoin (usually) you have to pay local VAT tax (in local fiat currency), because because national countries usually accept tax payments in currencies issued by their countries (and not in foreign currencies or currencies Alternatives), in some legislates there are exceptions, of course, but very rarely.
If you exchange cryptocurrency enough exchanging, usually this transaction is not taxed as long as you don't cash Fiat's currency.
Some national legislates require you to declare in your fiscal financial statements to declare they have Bitcoin. Some others don't.
Of course Bitcoin is cryptocurrency so Bitcoin owners know more difficult for institutions to track their transactions and they are not always in accordance with the rules.
I know my answer is not clear, but there is in the world of almost 200 countries, plus local legislation (such as US states, or different emirates in the UAE), so, unless you are more specific about your legislation, it is impossible to answer.