Gift Certificates are handled differently than other inventory items. It is a liability rather than income. You are taking money and holding it until the Gift Certificate is redeemed.
Selling a gift certificate does not update the Daily Sales Summary totals.
Running a sales report by dept/cat will exclude the gift certificates
Even running a sales report by Inventory: One Item GIFTCERT will not report any sales. The screen will begin to generate a report and then just blink away.
To determine gift certificate sales for a given time period, go to Manager: Gift Certificate Manager. Choose to print the sales report.
Another useful report is Accounting: Reports: Outstanding Gift Certificates. This will give you an idea of how many gift certificates may never be redeemed.