mm-purc ord. is in 3 decimal pts.want po value & all fi docu. in 2 de. pts.

we have created po with unit rate in 3 decimal points. As a result of this we get po values and all subsequent documents with 3 digits. Please tell how to configure so as to get 2 decimal points in purchase order value and all subsequent FI documents while maintaining 3 decimal points in unit rate.