I got some poptarts and the box was tampered with but I didn't think nothing of it...

Well, today, a few days after, for some reason I decided to check the packaging and all the remaining poptart packets (3) have a small hole on one side... all about the same sized holes...

So, I really feel I should get these tested to make sure... where, how, do I do that without spending a crap ton of money?

You take it back to where you purchased it and inform the store manager. Or you get to an emergency room to be checked if you have already consumed the product, taking it with you pronto.