1. A method of modifying a document comprising: providing a tangible computer storage medium; providing an original transaction document stored on the computer storage medium selected from the group consisting of an invoice and a vendor bill; providing a general ledger stored on the computer storage medium, the general ledger including original transaction postings corresponding to transactions contained in the original transaction document; providing a processor configured to access the computer storage medium; generating a new transaction document using the processor that is a copy of the original transaction document in response to a command to edit the original transaction document, wherein the new transaction document includes all of the transactions contained in the original transaction document, and the transactions of the original transaction document are selected from the group consisting of a product sale, a credit to an account and a debit to an account; modifying at least one of the transactions in the new transaction document using the processor; saving the modified new transaction document on the computer storage medium; nullifying the original transaction postings in the general ledger using the processor comprising posting one or more canceling transactions in the general ledger, each of which operate to nullify one of the original transaction postings in the general ledger; and posting transactions of the saved modified new transaction document in the general ledger using the processor.