Filled up with petrol today.

[annadomino]

Why oh WHY can they not display the price in whole pence. They surely cant think we are enticed by £1.29.9 a litre, rather than £1.30, they are kidding no one. It makes me bloody minded, I want to go in each and every one with a can, buy 2 litres and ask for my 0.2p change.

[sherrardk]

I wouldn't like that - it costs £90+ to fill my tank.

[joggerjayne]

Yeah, mine too.

That's a bit of a down side.

I usually refill after I've used a quarter of a tank, so it stays fullish.

[Clanad]

All the answers so far probably have validity, however, here in the U.S. an alternate answer is plausible... Back in the day, when the gasoline was sold from the distributor to the vendor, the gas was placed in above ground tanks with ill fitting lids on them at the vendors store (often a hardware or other coutnry store). The pumps were a hand driven affair that pumped the gas into a tall glass containe on top of the hand driven pump. The glass container was marked in graduations for gallons, up to about 10 gallons max. All this greatly contributed to the shrinkage of the volume delivered from the initial supplier through evaporation. To make up for this loss, someone came up with a typical, average, summer time evaporation rate loss. The mathmatics involved amounted to 9/10ths of a cent per gallon. Hence, the final seller sold his product at so many cents per gallon "plus" 9/10ths of a cent (US) per gallon tacked on for the shrinkage...
The added near penny was retained when mechanical pumps were introduced and underground storage was invented. (By the way, we all know the best time of the day to buy petrol (as ya'll call it) is early in the morning or late at night when it's cool, don't we?)

[TTG]

Don't fill tank to full...it's saves money (a little but it helps). Car does not have to carry heavy full tank of fuel.

[joggerjayne]

Golly, TTG ... I hadn't thought of that.

[jno]

Clanad, given that it's all in underground tanks, does temperature really make much difference?

[Clanad]

Yes, it does make a difference, jno. If the cool gasoline from underground is put into a tank that's quite warm, there will be more venting as it expands, hence a lot more evaporation than if you put it into a tank that was still cool, as in the early morning or late evening...