I'll take a stab at it based on common sense which may not apply here since most states, counties, cities are looking for ways to "enhance" their revenue...
I think it depends on whether you file a Schedule C form or a Schedule D form on your Federal tax return (assuming that you do file a Federal return.)
Most folks file a Schedule D. If you do, it probably won't be a problem, but you should check anyway.
If you file a Schedule C (you probably have elected trader status with the IRS) then you definately are operating and running a business and would be subject to tax at all levels (city, county, state, assuming if there is a tax in the first place.)
For example: If you live in Los Angeles, the city shares information with the California Franchise Tax Board. You would not only pay state taxes, but City of Los Angeles business income taxes as well.
Research this issue very carefully, because you don't want to get a letter like this one:
http://www.ci.la.ca.us/finance/pdf/AB63/Notification (3-4-04) A.pdf
Notice how they call it "Tax Discovery Program"
