To acheive a 5" finished 9 patch you would need to cut your individual squares 2 & 3/16th inches square (being 1" & 11/16ths plus 1/2" seam allowance) and even this leavesyou 1/16th" out. It would be much easier to use a finished measurement easier divisable by 3: i.e. 6" finished, using 2" squares.
If 5" finished is essential,you would have to make that minute adjustment either by adding the 1/16th to middle three squares or forgetting it as it is so minimal, --- haven't really got an answer for that one.