Am I propagating an actual Mint plant or is it a Pennyroyal plant?
it's from a grocery store.
The mints are somewhat variable, and the many species and hybrids tend to cross a lot, but pennyroyal has a couple of characteristics that might be helpful: the leaf is generally small, much smaller than the leaf in your last image, and the flowers tend to be widely spread out along the stem. Based on the leaf size alone it is likely not pennyroyal, and you would need to grow it on in regular soil to allow it to flower to check the inflorescence.
We consume mint in such tiny amounts that the downsides are few; we could also say that apples and potatoes are toxic from a certain point of view - who wants to eat a bucketful of apple seed strychnine or potato skin solanine? Many gardeners would just have a little nibble to see if it had any nastiness.
This is the wrong forum for advice on toxicity; gardeners as such are not qualified to comment on that, talk to your doctor or nutritionist. All mints have a reputation as possibly harmful either to humans or animals since it is relatively easy to get concentrated oils from the whole mint family.