Do you have to keep a copy of the sales and invoices?

It is the business's responsibility to maintain a complete set of documents with regards to the sales and purchases. You are not suppose to claim any business expenses without a copy of the supporting paperwork. Regarding GST, the law states that if the price is greater than $82.50, you cannot claim the GST unless you have the invoice showing the GST clearly on the invoice.

Is it permissible to maintain electronic copies of your documents?

Yes, and in fact it is encouraged, as long as:

Backups and Security

If you maintain an electronic document system, then you must:

What are the rules for keeping historical data?

The general rules are as follows:

Legal receipts must contain: