There should be tax calculation for individual store. The tax should be calculated on Sub total + restaurant charge - discount and not on including delivery charge.
For example an
item cost 100
restaurant charge is 10
discount is 5
delivery charge is 20
Tax rate for that restaurant is 5%
Tax should be calculate on (100+10-5) =105
How you are managing this issue, Because with this how we can work in indian GST System. Because we cam't charge 5% gst on delvery charge.