1. A method for electronically validating invoices, comprising: electronically receiving an invoice corresponding to a transaction between a purchaser and a seller; determining a purchaser tax jurisdiction and a seller tax jurisdiction for the transaction; determining a category of the transaction based on the purchaser tax jurisdiction, the seller tax jurisdiction, and a set of categorization rules; validating a tax rate indicated on the invoice based on the category and a set of validation rules; and determining whether the invoice is valid based on the validating.