I'd like to provide how an estimate works, Diane18.
An estimate is a non-posting transaction. You create this when you give your customer a quote or proposal for the work you plan to do. After you're done with the work or if you're ready to bill your customer, you'll add the data from the estimate to an invoice.
Thus said, you're unable to record a deposit against an estimate. You can record it against the invoice. You shouldn't cancel the HST on the invoices since it won't calculate on the estimates.
I've got you articles for your reference:
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