Yes it's highly unusual to quote prices in fractions of penny- but that doesn't mean there's no reason why items like fuel can't be sold at such prices.
For shops/pubs etc there is simply no reason why they would choose to price everyday items in terms of fractions of a penny . This is because in the main the quantity is fixed (you buy one tin, a 1kg pack, a litre bottle, a pint, etc).
Some items are sold loose- eg sliced ham. They could in theory charge for example 1.2 p a gramme. They would be "allowed to" but there's no point: no-one buys a single gram and anyway it's easier for customers to understand a price as �12 a kilo or �1.20 per 100 grammes. If you ask for 100g they give you something close, round down to the nearest penny and ask if you are happy with that quantity. So for example 263.4 p is rounded down to �2.63.
For fuel the price is competitive and people will shop around to save a fraction of a penny per litre so garages charge accordingly- eg 110.9p a litre. If you want , leslock and Corbyloon, you could insist that they round yours up to 111p!
Yes Corbyloon, your garage might have a minimum of 2 litres, and if you went to the trouble of measuring out exactly 2.00 litres they would round price down to nearest penny.
So what's the problem? Why does the issue trouble Leslock and Corbyloon) so much? Where is the 'con'? And what's the alternaive- introduce a law forcing garages to round prices up to the next full penny per litre!