A till screen you never have to scroll
At a busy counter a scrollbar is a lost second and sometimes a wrong tap. The register is built so everything fits one screen at any size — by scaling the whole layout to the glass, not by hiding half of it below the fold.
Watch someone work a counter at a rush and you see how little slack there is. A dish, a modifier, a total, a tender, next. Anything that adds a step — a menu that runs off the bottom of the screen, a button you have to scroll to reach — is not just slow, it is a wrong tap waiting to happen when the queue is six deep.
Fit the screen, do not hide the screen
The easy way to "fit" a busy layout is to push the overflow below the fold and add a scrollbar. That is not fitting, it is hiding, and it moves the problem onto the person least able to deal with it mid-sale. The register does the opposite: it treats the whole till as one layout and scales that layout to whatever glass it is running on, so the same screen that fits a big countertop display also fits a smaller one — whole, at once, no scroll.
One screen is a discipline, not a default
Holding to "everything fits, always" forces good decisions everywhere else. It stops a menu growing without limit, keeps modifiers to what a dish actually needs, and makes every new panel earn the space it takes. A feature that would only fit by adding a scrollbar is a feature that has not been thought through for a counter.
None of it matters if the person has to look for anything. So the measure is simple and unforgiving: if a member of staff ever has to scroll to finish a sale, the screen is wrong, not the member of staff.