Kat,
I would not use separate fields for the database, but rather use the aggregate of all the tolls and put that into the database as 'Tolls'. If you need to tie tolls to a specific number, don't use a specific field called tolls but rather use general expense column and use a name field to define the expense. Make sense?
I can tell you that using separate fields will become a nightmare trying to tie them to a specific run.
Example, Say I had to go from Chicago to NYC, I had a few tolls in Chicago, one in Indiana, one for Ohio, one for PA and then a few in NYC - this is one run. I then went up and down 95, in and out of NYC, then up to Connecticut then again down to Maryland, I think I could easily count 30 receipts and this was two weeks into the month. This is not uncommon for us.