When you gotta go...

Is it ok to use a chain store when you only leave something rather than buy/take something? So we are well into our month of Localvorism. We have not cheated thus far....although I do have a question. Last weekend we were headed to the natural food store and right next to that is a typical big box grocery store. I knew that the local store did not have a public bathroom....but I also know that the big box grocery store did. Since I only used their bathroom...I don't feel it cheating as no money left my local economy!