Hello. I would like to use UoM to group a bunch of item into a single product. I had a concern about how the UoM works. Let say that I create a new measurement called "rolls", which consist of 5000 units. I set the  Unit of Measure name to "rolls", selecting "unit" as category, selecting  "Bigger than the reference Unit of Measure" as its type, and set the ratio to 5000. I also set the precision into 1.0. And then i set a product default measurement into "rolls".
I tried to set the quantity in delivery order to 9900 unit (since it mean 2 rolls, as 1 rolls consist of 5000 units) and it work perfectly as at the reserve it became 10000 unit ( exactly 2 rolls ).
However ,  when I tried to set the quantity to 5100 unit in delivery order, it was rounded up to 5000 unit ( one roll). Is there anything I can do to make sure the round up goes to the 10000 instead of 5000 unit? Or is this not about UoM? I would rather send extra product instead of less than the required.
Many thanks.

I used odoo v12.00