I get discounts on gas purchases from a local supermarket (such as 10 or 20 cents off per gal. at the pump) - should I enter the full price and put the discount in the notes, or just enter in exactly what I paid per gallon after the discount? There are times when the stars align and I get more than a dollar off per gallon, which might make the calculations less meaningful. It makes no difference to me which method is preferred - I'd just like to provide whatever is most useful for other users.
I tend to think for price, it's most useful to yourself (and it varies widely around any single country as well as around the world), so I'd say track what you really paid and use the notes field to remind yourself of how you got such a discounted rate.