12:00 - after a delightful morning checking out the history of genocide in North America, you decide to drive the Turquoise Trail (NM14), a national scenic byway, south to Albuquerque. You stop to wander and eat lunch in Madrid, NM. What's the sales tax rate? Wrong, you're no longer in the city of Santa Fe, but Santa Fe county.
17:00 - you arrive in Albuquerque and go to buy something at a regular store. What's the sales tax rate? Ah, now you're getting it: you don't know, because now you're in Bernalillo County, NM.