Sales Tax/Freight on PO - Best Practices

Hi everyone,

We are on Peoplesoft 9.1. Wanted to see at what point in the process you add Sales Tax and Freight to a Purchase Order? Do you typically do this after the invoice is received, and PO is already dispatched (since you will know exact amounts)?  Or do you have this information loaded before Dispatch based on an estimate?

Just want to see how other companies handle to compare to our business process.

Thank you

Pete