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 indicating interstate sales transactions on which a seller does not collect a designated tax, such as a sales tax. This database is part of a computer network which organizes and stores the data in the database and automatically sends out tax due notices to purchasers when data in the database indicates that an interstate sale has taken place and no designated tax has been collected from the purchaser by the seller. This database can also be updated to reflect payment of the tax indicated in the tax due notice, and can automatically remit appropriate revenues to a revenue agency when the tax due notice has been paid. One implementation is also collecting a simplified tax on all interstate sales transactions, and then storing data in a database indicating this collected simplified tax and data as to a revenue agency entitled to the tax based on the purchaser, the state of residence of the purchaser, etc. Based on this data in the database, the collected simplified taxes can be proportioned and routed to the appropriate revenue agency.