We don't total quantity as it usually doesn't make sense. Say that you had a trip that 50 miles, but you also had 2000 nails in your expenses it wouldn't make sense to have a 2050 for the quantity. It really only makes sense for total time (duration). What you can do is set a specific expense (e.g. your Mileage expense) and use the CSV export and open that in Excel or Numbers to get totals. If you don't have the CSV option on that is at Setup -> Reports -> Format and set to "HTML and CSV".