Show the top 5 items in percentage of the total in pivot table

Item,Quantity

A,1

B,2

C,3

D,4

E,5

F,6

G,7

H,8

I,9

J,10

Is there a way to show the top 5 items in percentage of the total in pivot table? When I click 'show top 5', the total changes to the sum of only the 5 items, what I actually want is the sum of all items (i.e. item J will be 18.18% instead of 25%)