Always expect you to have loose change, it's their shop,up to them to have cash in tills to run it.
Here's the phrase Mr Atch gave me for that situation:
'To jest sklep. To Pan/Pani powinna wydać mi resztę a nie ja Pani!'
This thread has already provided two useful supermarket vocubulary phrases for the learner of Polish :) Not that you need it Dolno. By the way the other day when I was rambling on about something, I most unintentionally lumped you in with the 'hysterical' Poles on the forum. You're also an exception, cast in the same mould as Ziemowit, a proper Polish gent!