[Collect Cash Payment] Add Exact Amount button and show order total prominently on cash screen

[joshheald]

We have some suggestions for improving the cash payment interface

1. Add an Exact amount button to reset the recieved button to the order total
2. Show the Order Total more prominently when we have space

Context: 6kkCwI9VOEYcidp6UT5bln-fi-1108:29269#719681467

[dangermattic]

Thanks for reporting! 👍