Supermarket app that allows adding items to a cart and then applying discounts on this cart.

The app does not cover this questions:

• does fractional money exist?
• when (if ever) does rounding take place?
• how do you keep an audit trail of pricing decisions (and do you need to)?
• are costs and prices the same class of thing?
• if a shelf of 100 cans is priced using “buy two, get one free”, how do you value the stock?