you need to send a chr(7) to the printer.

make sure that

set printer to lpt1: && or com1: / com2: / lpt2: whatever is appropriate
set print on
set console off
???chr(7)
set print off
set printer to

this is generally integrated with the printing of a receipt.
i generally find that you have to think how the app will operate in practice and do the drawer opening before the till receipt is printed to give the operator time to put the money away and give change etc. will the receipt is printing

regards

Colin Burton