Honestly, I'd hesitate to whip out a pocket knife inside a "dollar store". Sad to say, but like "Waffle House" employees, the people there have seen some shit. One one hand, a well-behaved, clean individual that doesn't look like a tweaker shouldn't raise any alarms if they pull out a pocket knife (tool) to open a box that they asked you to open. Believe me, they've seen worse. OTOH, you might have a clerk that might have a PTSD reaction because of all the crackheads that have threatened/robbed/assaulted them in the past. I know that not everybody here does or wants to carry a non-threatening blade in addition to a main EDC, but I'll always advocate for doing so. A traditional slipjoint, SAK, or some sort of mini modern knife. If I were in that situation, I'd have used my Spyderco Ladybug, or, if I had it with me, my Magnus SlideClick utility knife.
I might act differently in, say, Albertsons or Ace Hardware though. Personally, I don't find myself inside "dollar stores" very often anyway.
ETA: It's entirely possible that the employees, because of the inherent dangerous nature of their job, aren't allowed even simple box cutters, for fear of them being used in self defense (and the lawsuits that follow). I'm sure all of us agree that those kinds of rules are BS, but they're an unfortunate reality of the world we live in.