You can try like this,
For this you need to create 2 expressions.
2. =(sum(Sales) &'
'& Num(sum(Sales)/sum(TOTAL Sales),'##0.0%'))
Then you need to Group these expressions and for the second expression check 'Relative check box', and uncheck 'Bar'.
And choose % sign in the number tab for the 2nd expression.
Make sure to enable 'Values on Data Point' in expression tab for both the expressions.
Hope this will help you.