Collecting County Taxes in USA, PA, Need help setting up

[KNSpeedFactory]

So we have our state licenses set up, but in some states there are county sales tax.  For example the state of Pennsylvania is 6% but if we ship to Philadelphia we are required to charge 2% county tax as well.  I have tried and tried but I cannot figure out how to do this.  The good thing is all Philadelphia counties have a zip code of 191XX so it would be easy to set up via zip.

Any help would be great