We store prices to three decimals, but we don't always display them at three decimals. If you go to your fuel-up log, you should see prices to three decimals.
We'd like the ability to support multiple vehicles via SMS, but we haven't found a good way to to do it yet. The Miles Price Gallons [Note] format is very simple, and we're reluctant to tamper with that. If you have to precede [MPG] with an arbitrary number that represents the vehicle, we feel like that adds too much complexity and would lead to failed SMS messages. So it's something we're thinking about.
Would you possibly be able to use the vehicle name instead of a number? I love the fact that I don't have to waste receipt paper, but it's only on my primary. The ability to assign a fuel-up to each car is a feature I am anxiously waiting for. But I'm willing to wait for perfection!
If you have your vehicles set up for odometer mode, you should be able to guess which vehicle it belongs to based on the mileage. This would work well for most cases, and maybe if you couldn't guess you can just send a reply asking which vehicle it was for.