Help me with a question of taxi cab etiquette?

The pharmacy in my college town is just a bit farther than I’d want to walk, so if I need a prescription, I’ll probably have to take a cab.

I’m guessing I will have to call a cab, have him drop me off at the pharmacy, do my thing, and then call another cab to come to the pharmacy and take me home. However, if there’s any way I can avoid having to do that, I’d like to, because it’ll cost me more. There’s a $3 flat charge at the beginning, then it’s $0.25 more per quarter mile (I think). So of course if I do what I said above, I’ll be paying that $3 charge twice.

I’m guessing it’d be really poor etiquette to leave the cab driver sitting waiting while I run into the pharmacy and get what I need, and then take the same cab back home, right? He’s not paid per unit time, he’s paid per unit distance, so he wouldn’t earn anything while waiting for me. But I would call ahead to the pharmacy so they would have the prescription ready for me so that I could just run inside very quickly.

What do you think?