Most USB connected cash registers will integrate into Symphony as long as they support your printer type (e.g. Epson, Star).
When you are in the receipt printer configuration, (under Preferences --->Peripherals ---> receipt printers, then there is a check box for CASH DRAWER SUPPORTED along with an ASCII code sequence that opens up the drawer during the proper transaction. List of codes can be found here: http://keyhut.com/popopen.htm
If you have the cash drawer checked on (and have the properties set to print receipts for bill payment) then when a receipt for payment is printed on the receipt printer, the ASCII sequence will be executed and open up the cash drawer.
Example setup:
Please open a ticket if you have any issues.