An effective and efficient system for recovering tax revenue. One implementation is to recover tax revenue currently not being recovered by storing data in a database (2) indicating interstate sales transactions (7) on which a seller does not collect a designated tax, such as a sales tax. This database (2) is part of a computer network (1) that organizes and stores the data in the database (2) and automatically sends out tax due notices (S3) to purchasers (5) when data in the database (2) indicates that an interstate sale has taken place and no designated tax has been collected from the purchaser (5) by the seller. This database (2) can also be updated to reflect payment of the tax indicated in the tax due notice (S3), and can automatically remit appropriate revenues to a revenue agency (4) when the tax due notice has been paid (S4). One implementation is also collecting a tax on all interstate sales transactions (7) by using a central facility that assists remote sellers in knowing what rate to employ for any given transaction and receiving and distributing collected taxes to the appropriate revenue agencies (4).