Add constraints on quantity
From https://discuss.tryton.org/t/different-purchase-unit-on-the-same-product/3332/7 We could have two modules (one for sale and one for purchase) that defines minimal and rounding constraint on the product/supplier.
For the sale it is a strict constraint on the line as it is a company rule that can be enforced. For the purchase we can only use it as a nice to have. So I think we should just adapt the quantity when the system create purchase line (from purchase request).