Excel formula shows shows -2.2E-13 instead of 0 in one case only. help

[hulk3rules]

I use excel to track my winnings at the sites I play at. I have a pretty simple sheet with the following columns in the picture below, date, start total, end total, proit, other. I use other for deposit, withdrawal, bonus, etc.



I use a formula for the profit column, C-B-E. Now for some reason today it gave me this number instead of 0. It works on any other day that it should total out to zero, as I show below. If I change the E column to any other value then the profit column shows what it you would expect it to show. Any ideas why I would be getting this number for just this one particular example?