How to adjust cart quantity automatically based on box quantity increments?

Hello,

Our store carries products which are sold in full box quantities. For example, sheets may contain 5 dozen per box, towels are 10 dozen, other items may be 3 dozen and so on.
We would like to adjust the product quantity selector to automatically increase the quantity based on these box quantity increments. In this case, if a customer wants to order 1 box of sheets, the quantity would increase by 5, if they want 2 boxes, the quantity will be 10 and so on.
We want to display the cost of only 1 dozen per product, and the total amount would update based on how many dozens are in a box.
We’re using the Minimal theme.

What is the best way to do this?

Thank you very much.