Rounding as per T001R

Dear Friends

In the pricing procedure , the field sub total we have a requirement 13 which is rounding as per T001 R in DIFF condition type.

Also in OB90 the logic is maintained : Co code - Currency - 100.

My question is how this Logic works during the operation ? what is this 100 meant for ?

A explanation with an example would be highly helpful to me.......