The only legitimate reason for taking your dog into the store is, in my opinion,
If it is so sunny and hot out that you cannot safely leave the animal in the car. But if its a poorly behaved dog, you should drop the dog off at home before you go back out to go shopping.
There are people who are fearful of dogs and other animals. If they are in the store shopping, and somebody comes in with their dog, it could cause distress. I know, if someone came in wearing their Burmese python, I would not be thrilled.