Sales unit without decimal release quantity with decimal

Hello,

I sell ropes, by meter, or by complete reel of 100m.
So I've my unit "m" for meters, and a unit R100 for reel of 100m (with conversion 1 R100 = 100 m).

When my customer ordering 1x R100, with WMSIII, if I release the order in the warehouse, with only less than 100m in inventory on hand, 58m for example, the system can create a wave for 0,58 xR100.
I want only full R100 to be delivered, that's why I fill my unit with 0 decimal. But it doesn't work.

Somebody know why ?

Thanks