Round off of unit price figure on PO

DEAR EXPERTS ...i had facing a diffrent kind of issue recently ....... in our client when ever we purhcase the item so most often we have to add the 16 % gst (general  sales tax) on each item now because of this gst most of the item the unit prices comes in point and i use to count two digits after points say 22.20 even the actuall answer come 22.209 but here i refused 9 to select ..... last time while makind the PO i had faced this kind of issue when i m  manually calculating the total amount of