Don't freight your answers with any notions of what you're "supposed" to do, and just see where your feelings point you. It can feel weird to be so formal about it, but if you're not used to doing it, then there's no shame in retraining yourself.
Carolyn HaxI think a person who arranges the event and orders the food also picks up the check - even the birthday person, even when people at the table insist on paying for the birthday person.
Carolyn Hax