Even though it is a small amount of money it adds up and you should take advantage of every deduction that you can
Miles have to be recorded at the time that they are driven.
(Not while driving the car though)
You should print the free mileage log on this site.
The Internal Revenue Service can be very specific about accurate record keeping.
The IRS will not let you guesstimate.
As an example, if you drive your car for a charity 100 miles a week you should take a medical mileage allowance every week.
After a year of doing this every week, it adds up. It doesn't seem like much at first, but when you add it all up it pays off.
Again use the mileage log.