There's actually written policy on this giving all students the right to view their marks. Just in commerce the faculty is very open about it and publishes dates you can go and review your exam but other faculties require you to request it. I'll paste the relevant parts of the assessment and results policy below (approved as of November 2017):
4.110. Students may request access to their examination scripts by making a request in writing to the dean/subject coordinator by the end of the second week of the following teaching period.
4.111. The dean must provide appointment times for students with examiners after return of results on each assessment component to allow students to address any problems / poor performance and/or be able to access support services of the University provided for them if required.
4.112. The chair of the BoE must ensure that examiners in each subject are available to provide feedback to students about their performance after the release of results in that subject.
4.113. If requested, examiners must provide students with a detailed account of their marks for a subject, including the marks awarded to each assessment component and the calculation used to determine the final overall subject mark and grade.
You obviously should not go checking every single exam you do as it's a waste of time, but if you're ever really really sure after doing the math and being conservative that something is not right then it's worth checking.