Reviving this: I have never personally had an issue with this at any dealer (whether leasing in PA our out of state). That is, they have always correctly built the deals so that tax is NOT applied to any rebates or incentives (regardless of type).
Since others seem to have issues with this, thought it would be helpful to find the reference in the PA tax code:
tldr: As long as they are point-of-sale / instant, and referenced on the lease contract, then they are not taxed.
(2) Discounts. Amounts representing on-the-spot cash discounts, employe discounts, volume discounts, store discounts such as ‘‘buy one, get one free,’’ wholesaler’s or trade discounts, rebates and store or manufacturer’s coupons shall establish a new purchase price if both the item and the coupon are described on the invoice or cash register tape. An amount representing a discount allowed for prompt payment of bills which is dependent upon an event occurring after the completion of the sale may not be deducted in computing the tax. A sale is completed when there is a transfer of ownership of the property or services to the purchaser.
Further, from PA dept of revenue:
"The reduction coupon has to be an instate rebate (Not a mail in rebate/coupon). If it is an instant rebate/coupon that states it is lowering the amount of the purchase price and it states it on the lease/Purchase contract it will lower the price of the purchase price. Which changes the total price of the vehicle and the amount of tax.
If it does not met the above criteria then it would not change the purchase price and sales tax would be charged on the original purchase price even if there is a coupon that reduces the total."