Tankering is not just done for the purpose of saving money at destination, often the airline is contractually obliged to buy a certain amount of fuel per year and if they overestimate that amount then you find yourself carrying extra fuel just for the sake of buying it. I have tankered fuel to the Gulf before!
Generally in shorthaul we would try to estimate the amount of fuel required for the trip home and then load enough fuel so that we landed with that amount plus about 300kg (for APU burn). If you are leaving the aircraft downroute then you find yourself second guessing the fuel decision of the chaps who are taking over so we usually plan to land with a bit more to give them more flexibility.
In longhaul it is not usually possible to carry round trip fuel, so we plan to land at a tonne or two below max landing weight to allow for any enroute fuel savings.
Another consideration is the weather at your destination. If it is a bit chilly with high humidity or precipitation, then you can easily get icing on the wings as the extra fuel you have carried has cooled to subzero temperatures during the cruise. Deicing an aircraft will easily wipe out any cost savings made by tankering and so we would not tanker in such conditions.