Property and Sales Tax Data

I have a question pertaining to the tax data, specifically that relating to sales and property taxes. How are these values calculated in IMPLAN exactly? Both of these tax rates are extremely variable within a county so I was curious what data is used to arrive at the tax data after running an impact analysis through IMPLAN? Is it based off a weighted average of the different tax rates within all the zip codes residing in that county or something along those lines? How does IMPLAN account for the differences in online sales tax rates as well? This would greatly help my understanding of the data and further my understanding of the results that IMPLAN has calculated for me to be relayed in our reports. Thanks.