You need to keep a daily log book with beginning and ending mileage for tax purposes. For more information, hop on over to the New Mystery Shoppers area and read the tax thread near the top. You are now in business for yourself and need to keep business records.
Also, you can use the "search feature" here to look up "taxes" for "all dates," for tons of discussions on the subject.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.