They can't really track your bitcoin transactions if you don't allow them to.
If you operate with bitcoin only and cash, they you can avoid paying any taxes, for an example, if you hold your whole amount of money in bitcoin, and pay with bitcoin for things that you can use bitcoin for, and for things that you can't pay bitcoin, just convert the bitcoin to cash privately ( local bitcoins might be the solution) and pay with cash, the only problem would be when you want to buy big property such houses and cars.
Do you know a lot of supermarkets that accept bitcoin payments? You're talking about perfect conditions. But this is not. All users in order to make a purchase of goods for bitcoins are forced to use bitcoin to Fiat exchange operations. At this stage, any amounts become subject to taxation. This situation is not only in America but also in any other country.