I don't think there is a valid way of calculating the shipping costs based on grand total (or maybe I'm missing something), because the shipping cost is included in the grand total.
So in theory you can have cases when you can have 2 shipping costs that are valid.
Here is one.
Let's say you have the following rule.
All orders with grand total below 100 have the shipping cost 0 and all orders above that have the shipping cost 5.
If the subtotal is 99, then you qualify for both cases.
If you apply the free shipping then the grand total is still 99 - so it's valid (below 100).
if you apply the shipping cost of 5 then the grand total is 104 - so it's still valid (above 100).
I think the best approach on this is to use the shipping cost based on subtotal and adjust the shipping prices to fit your subtotal intervals.