Déjeme
contar...
sí,
trescientos
veinte.
Perfecto,
muchas
gracias.
DEH-heh-meh kohn-TAR... see, trehs-SYEHN-tohs VEYN-teh. pehr-FEHK-toh, MOO-chahs GRAH-syahs.
Let me count... yes, three hundred twenty. Perfect, thank you very much.
It's perfectly normal and expected to count your change in front of the cashier. No one will find it rude.