It really depends. If they're simply putting their receipt in their purse, and change in their wallet, I'm ok with that. The extra 30 seconds don't make a difference. But then they do that, then start diggin in their purse for soemthing else, then realize they have a coupon they didn't give the cashier, or generally are taking longer than it should, then I get a tad impatient.
I had one yesterday, but leaving the grocery store. She had a full cart in front of me, which she was having trouble manuvering due to several cases of water. She was also moving veeeeeery slowly, while perusing her receipt, as she walked out. She then got to the first set of doors, got halfway through and came to a dead stop. THAT makes me crazy. I get that you might want to get your keys out so you can open the trunk etc. but please don't block my and everyone else's way.