You don't need to pay tax if you are dealing with small amounts. If you cash out and spend it on your daily cost or buying clothes, phones, TV's etc. you are fine. But if you buy something more valuable like cars, houses and such your government will ask you where did you get it. In that case, paying taxes would be advisable. There are some tools that US government or others can use to track crypto transactions and connect them to you exchange profiles, which are verified with documents that you provided them when you registered.

https://www.chainalysis.com/