Don't move as they may come in a pack for the cash register (3,5)

I believe the answer is:

lie still

I'm a little stuck... Click here to teach me more about this clue!

'don't move' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'they may come in a pack for the cash register' is the wordplay.
'they may come in a pack' becomes 'lies' (I've seen this in another clue).
'for' is a charade indicator (letters next to each other).
'the cash register' becomes 'till' (I've seen this before).
'lies'+'till'='LIE STILL'

'as' is the link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.