The IRS treats staking/mining as income. This means that you're supposed to pay income tax on all the ADA you receive through staking.
If you receive a staking reward of 10 ADA, and at the time of you receiving that ADA, one "coin" is worth $0.8, it means that you're supposed to report the $8 as income when you file your taxes (and pay income tax on it).
You might be one of those people who don't care to report, but here's the problem: if your ADA stack is worth a significant amount of money one day, and you decide to sell, there's a decent chance that you'll get audited. You'll then have to explain where those ADA came from. If they find out that you were (in their eyes) not reporting income, you're in for a hell of a ride.
**I’m not an accountant, so I can’t address specific tax questions. Please check with a tax professional if you’re unsure about your situation.**