Auto Grading Rounds Off Grades In the Dashboard which Results to Slightly off Grades after Sync

## Bug report form
### Steps to reproduce
1. Create a Hypothesis assignment in Blackboard.
2. Set the Maximum Score of the assignment to 15.
3. Enable auto grading and set the required annotations to 3.
4. Have a student post one annotation.
5. View the assignment in the LMS dashboard
6. Sync the grades
7. Check the grade in the gradebook.

### Expected behaviour
Tell us what should happen.
In step 5, it should display 33.33%

In step 7, it should display 5, since 1/3 of the maximum score (15) is 5.

### Actual behaviour
Tell us what happens instead.
In step 5, it displays 33.30%, which is slightly off when you represent 1/3 in decimals.

In step 7, it displays 4.99, which appears to the product of 33.30% and 15. The actual product is 4.995. The gradebook in Blackboard Ultra shows 4.99 only, but in Blackboard Original, it shows 4.995.

### Browser/system information
Chrome 152
MacOS 26

### Additional details
Related ticket: https://app.hubspot.com/contacts/6291320/record/0-5/48557511538
This issue isn't specific to Blackboard. Blackboard just doesn't round off grades, which is why it exposes the small discrepancy in the scores.

Reproduce the Blackboard scenario from the issue, then trace the auto-grading percentage and grade-sync entry points involved in steps 5–7. Done means the dashboard displays 33.33% for one of three annotations and the synced grade is 5 for a maximum score of 15, without regressing other LMS behavior.

Written by the indexing model from the issue text.