That's cool! Though, one thing to consider. If it takes you 10 or 15 more minutes to save $5, is that really worth the amount of time to save that small amount of money?
For example, in my Honda Civic I have a 10 gallon tank. Even if the price of gas is $0.20 higher than the place 10 min down the road, that only saves me $2.00 for 10 min of time/work. Now, if I only made $12/hour, I'm breaking even, but if I make more money than that per hour, I've in fact made my time worth less. Even in my Pathfinder, I've only saved $4 because it has a 20 gallon tank.
I'm not trying to burst your bubble. I think that's a great tool, especially if you happen to be heading in the direction of cheap gas or pass by the cheaper station often. You now know that it's valuable to stop there, eventhough you may not need to fill up at that moment.
Just trying to give a lesson in the value of your time.