I'm guilty of the same behavior, although I am not OCD in other ways. I have tracked all of my cycling miles and other fitness activities for many years, starting from my days as a runner. Although I no longer run, I track walking miles and other exercise as well. When cycling, I usually extend rides if I am close to 30, 40, 50 ... 100 miles, etc. No real reason for it, just makes me feel like I've accomplished more. I also often extend rides or other exercise to reach 5 minute increments, simply because my exercise-calorie tracker uses 5 minute increments. Thus, if I ride for 49 minutes, it only gives me credit for 45 minutes of exercise, which sucks!