You are right you need to have an intelligent cash drawer for that . Like an IBM 46nn Series or NCR which use interrupts to return info about the status of a cash drawer(all devices are directly pluggged into the PC eg Drawers,Scales,Printers,Walking Messages Ect). If you are using a normal cash drawer plugged to a printer I dont think you can do it. All the printer generates is a pulse which triggers the drawer open.

Regards,
Fred