Incorrect total score calculation

Our exam has a maximum score of 4000 points, divided over 13 questions with each question have several rubric items. The smallest items are still multiples of 10 or 25. Much to our surprise we had total scores like 2376 en 3434. A total of 170 students got the wrong total amount of points (all off by one) and we had to redo the score calculation in Excel based on the export and reupload the results to Brightspace. Is Python doing funny things with numbers here?