It sounds like you want the shift button to act as a stay down instead of pop up type. this means it will stay where you set it until you set it back to the other level manually. you need to set this in the shift programming. I don't have the codes for this model. Check your manual for the setting.
If you don't have one, C-tech collective have an NX-5400 programming manual listed, so it should be in here:
http://the-checkout-tech.com/manuals/cashregisters/uniwell1.php
Registerman, April 2011
