Can I refuse to go grab paper towels when I'm asked to do it?
What makes you refuse to get paper towels?
I think they are stupid to expect it from me.
It's rude to refuse a simple favor. If you feel like you're being taken advantage of, you should communicate that. Maybe that way you can figure out a plan to split chores and errands.
I don't need to feel like that to act like this. It's not even my job.
It is a favor, not a job. If someone asked you to do something simple for them that you really want done and they said no, how would you feel? It's nice to do things for people sometimes even if it doesn't seem like a big deal.