At least in the United States, as far as I'm aware, you can use any currency that you want. However, the government and IRS only accept tax payments in US dolla

At least in the United States, as far as I'm aware, you can use any currency that you want. However, the government and IRS only accept tax payments in US dollars. Under these laws, you could transact in cryptocurrency all you want, but you'll need to pay sales tax, income tax, and other relevant taxes in dollars.