@rengb121 It really depends how much further you have to go to buy fuel?
If your car has a 60 litre tank, you'll save 60 rp for every rappen/litre discount if you brim the tank from practically empty.
Assuming 6l/100km, and about 1.80/litre fuel cost, your 60rp saving will go about 5km further, or 2.5km each way to get to the discount. Thus, you have to travel less than 2.5km further than your closest station per rappen discount to get any savings.
For example, let's consider if your closest fuel is 1.80/litre but, if you drive 5km further, it's 1.78/litre. Effectively there is no difference financially, since you burn additional fuel equivalent to the savings to travel the extra 10km to reach the discounted source.
You can do the math, but as a rule of thumb, you have to go less than 5km further to save with a discount of 2 rappen/litre.
Obviously different cars/fuels have different efficiencies, as does different driving styles/routes. But as your litres/100km goes up, the distance you can go to justify savings goes down.