During the sales tax remittal period you need to get the total sales of that period.
In order to have an easy way, this report allows you to see invoices for a period:
https://erpnext.eco2.ca/app/query-report/Sales%20Register
On the bottom of the list, there is the total for each column: sales. GST, PST and HST. All you need to do is choose the period, and it will calculate the rest.
Report: sales, gst, pst, hst totals