Hi James,
In the SA you don't have the rounding profile field. It uses the data from the material master.
So having a different rounding per SA is at least to my knowledge not possible using SA's.
James using the SA together with a quota arrangement you can have the rounding profile kicking in per material vendor combination.
In the quota arrangement you can enter the rounding profile
If you only have a single source you just enter 100 as the quota