How in the hell is the I.R.S. going to know if you're mining unless you stand up and say Ummm Hello here take my money please i'm an idiot!
Dont worry, they can find your IP.
It's called a VPN.
Yeah, they can partner with VPN providers and get them to hand over your data, that's where TOR with a TAILS Live disk comes in. They usually don't try to tax you for your mining revenue unless you are a corporation like Butterfly Labs though.