Also, the federal isn't a credit, it's a discount off of msrp. The state is a deduction, so you typically have to carry it a few years to see the full benefit. Just in case anyone is curious.
To clarify, there _is_ a $7500 federal tax credit, but Nissan just takes it themselves and passes those savings directly to the customer, which is what makes it possible to indirectly use the credit when leasing instead of purchasing.
The Georgia $5000 tax credit is indeed a credit, not a deduction, but it's a _non-refundable_ credit, meaning if you owe less than $5000 in taxes, you can only take a credit for that lesser amount the first year (so you're taxes are $0 instead of negative), but you get up to five years to take the full amount of the credit (in the case of this particular credit).
The Georgia credit applies in full even if you lease instead of purchase. I doubt that's what the legislature intended, but it's the case nevertheless.