Most cashier shifts are fairly easy, and the majority of customers are nice people. There are, however, not a lot of hours given, and it can be hectic during rushes. Be prepared to learn a lot about taking care of animals, because you'll be handling and helping customers with all of them.
The management is usually easy going, from what I've seen of multiple stores I've worked at. Hardest part of the job is simply the daily maintenance and cleaning of habitats, but if you're a cashier that won't be much of an issue.