Usually, you must keep your records for six years from the end of the year to which they relate. This includes all sales and purchase invoices, and all other records related to your business operations and the GST/HST. However, the CRA may ask you to keep the invoices longer than six years. If you want to destroy your records earlier, you have to send the CRA a written request and wait for the written approval.

For more information, see GST/HST Memorandum 15.1, General Requirements for Books and Records.  

As a registrant, you also need the correct information on the invoices you get from your suppliers to support your ITC claims.

For more information, see Records you need to support your claim.