Actually there's a difference in United States income taxation between functional currency which would be the United States dollar, versus a non-functional currency. No tax advantage necessarily just the potential to lose capital gains tax treatment and instead receive ordinary income tax treatment which is a worse answer for taxpayers engaged in income-producing transactions or a trade/business. On the other hand, for individuals involved in personal transactions, (1) there is a small deminimis rule that prevents taxation for very small transactions, (2) there may be capital gain potential, however (3) there is also the potential to lose the ability to deduct losses as capital investment losses - because, non-functional currency Losses under a certain dollar threshold are subject to personal loss deduction dis-allowance. In short, we can't just assume being called a currency is the best from a tax perspective.

Edit #1- clarifying a point and adding the source of IRC Section 988.
https://www.law.cornell.edu/uscode/text/26/988

Edit #2 - Pinging @alhofmeister another tax writer on the platform for consensus (or divergence) on the point.