[nine_k]

This assumes that the scope of tracking is somehow naturally limited to grocery, and can't extend. Also, the technically easiest way to track grocery purchases can be by tracking all purchases, and then filtering out the non-grocery.

Let's generalize the question: what makes you uncomfortable about the government tracking all your (non-cash) purchases? They already know your income for tax purposes, and much of your large purchases, also for tax purposes. And if you need a pinch of stuff that's illegal, you're not going to swipe your debit card anyway. I suppose a court order will show all your bank operations history, should the government need it for lawful purposes.

So, if there's still anything left to preserve, we need to clearly articulated first, what that is.