That is not an error - it is just that Moodle rounds up. The 5 decimals is showing the total number, when you cut to two decimals it will round up. I do not know of a way to adjust that without hacking code.
Gradebook
Error in round grade
Αυτή η συζήτηση κλειδώθηκε κι έτσι δεν μπορείτε να απαντήσετε σε αυτή.