Minimum order Quantity

Dear Experts,

Client Requirement is , as per material basis they want automatic adjustment in PO qty .

Example : suppose in PR , Quantity is 8 qty . When i convert PR to PO , qty should be automatically 10 QTY as per material basis. if i given in PR 18 it should come 20 QTY . if i given 12 qty in PR , in PO it's should be come 10 qty

HOW TO DO THIS ONE , PLEASE HELP ME