You are working through your RCM books one by one (hopefully with a good teacher), learning a good amount of repertoire from each book, but decide that you’d rather save some money and not do every single exam in turn.
This is completely acceptable. In fact, some teachers even recommend to their students not to do every single exam, especially in the Elementary Levels (Prep to Grade 4). Once students get to Intermediate Levels (Grades 5-8), it might be a good idea to stop skipping, as the material gets noticeably more difficult. Also, keep in mind that starting from Grade 5, students need to complete and pass a co-requisite written examination in order to get their Certificate.