You are not Petty but calculative. As you mentioned you are well to do, I am sure these bills are peanuts. I am sure the parents are not dining at expensive restaurants or ordering exclusive dishes like shark find, bird nests or Abalones. Of course if they also bring along brothers, sisters or uncles and aunty, than you can voice out. If you are a Chinese race, than usually paying for the parents are sign of being under one roof. Respects to elderly like in law's etc. If you don't feel comfortable, just try not to go out together especially dining.