For the desktop version: Yes, you can do as many cases as many times as you want. After completing each case, you will be given a grade. If you do 10 attempts on one case, you will be given 10 different feedback scores. All attempts and their scores will be saved for your review. See the image below: at the grading menu, they will be listed by the time of each attempt. You can click on each attempt to view your feedback and score.
For the online version, the 1, 3, 6 month versions, you can do each case as many times as you'd like. The 12 month version has a 3 attempts per case limitation.