I run a tank nearly dry and then always fill up the same way.
It's the way I do it and I never, ever put 10$ at the time...that's just useless IMO.
The way a diesel tank is arranged, it's fairly easy to fill it up the same level everytime for max accuracy fuel economy calculations.
VW puts a vent button, that when you push it you hear air coming out.
That is called "venting" in dieseler's term.
When venting you fill up the tube that goes from the tank to the brim of the filler neck.
Mine holds 25 litres, most Golf/Jetta/NB will hold about 7 litres.
It's the way I and many TDI owners do it so it gives you a good idea of your mpg per tank to a pretty accurate level.
