The osCommerce Connector for TaxRates is an open source plug in that integrates osCommerce with Sales Tax calculations based on the zip code data downloaded from TaxRates.com.
Sales Tax is calculated based on the zip code of either the order shipping address (or the order billing address for digital goods) and the sales tax rate applicable to that zip code. The sales tax tables for each State in which a site has Nexus are available to be downloaded for FREE from the web site TaxRates.com
The plug in uses the shipping information and line item information from the osCommerce order, parses the sales tax rates from the tables provided by TaxRates.com to calculate the correct amount of Sales Tax to be added to each order.
Sales Tax on the shipping line item (assuming by public carrier) is correctly calculated for the those states that require shipping to be taxed.
Sales tax calculations performed on zip codes can not be 100% accurate. Sales sales jurisdictions are based on boundary data. As a result rates based on zip codes do not align perfectly with jurisdictional boundaries. But using this FREE service from TaxRates.com, sites can validate their business models, while depending on regularly updated "near rates" until sales volumes justify investing in a commercial service.
The plug in has concentrated on simplicity of install, admin, and operations. No osCommerce files require changing. Installation is to copy the files to the regular plug in directories, and configure in the same way as any other plug in.