the American state of Arizona passed a law to allow tax payments in Bitcoin
That's incorrect.
The Bill has been passed by the Arizona Senate and will next go through the Arizona House of Representatives.
By Helen Partz on Cointelegraph:
The bill has now been sent to Arizona’s House of Representatives.
If the bill is adopted, Arizona would become the first state in the U.S. to accept cryptocurrency tax payments by the year of 2020, as stated on the public record. The bill would allow taxpayers of the state to use “a payment gateway, such as Bitcoin, Litecoin or any other cryptocurrency recognized by the department, using electronic peer-to-peer systems.”