This question is inspired by large discussions about pros and cons of electronic sales records from real world.
It is sure that electronic sales records are not fitting to classical fantasy (that is more or less based on medieval age) - even if I decided to enrich fantasy by few elements from modern ages (but they are based on magic - and thus explainable by magic too).
However, sales records are documented even from medieval age (or older ages too, but those ones are quite rare).
Notches into wooden desks (or wooden rods or so), is one way. It was famous way how to record someone's debt drinking too (I don't know exact term from English language for this).
Any soft type of stone (instead of wood) would be probably usable too - and these records would be permanent, or at least fire-resistant.
What else materials (even fictious) could be usable to record sales - in medieval (and thus also in fantasy) regardless of form of letters? (because only few, well-educated people, can write - meanwhile much more people were able to count, at least a little)