See here - http://www.tax.ny.gov/bus/st/stidx.htm
Sales tax applies to retail sales of certain tangible personal property and services.
See the actual law section
§ 1101. Definitions.
(3) Receipt. The amount of the sale price of any property and the charge for any service taxable under this article, including gas and gas service and electricity and electric service of whatever nature, valued in money, whether received in money or otherwise, including any amount for which credit is allowed by the vendor to the purchaser, without any deduction for expenses or early payment discounts and also including any charges by the vendor to the purchaser for shipping or delivery, and, with respect to gas and gas service and electricity and electric service, any charges by the vendor for transportation, transmission or distribution, regardless of whether such charges are separately stated in the written contract, if any, or on the bill rendered to such purchaser and regardless of whether such shipping or delivery or transportation, transmission, or distribution is provided by such vendor or a third party, but excluding any credit for tangible personal property accepted in part payment and intended for resale.
Taxable Receipt - How Discounts, Trade-Ins, and Additional Charges Affect Sales Tax
Sales tax is calculated based on the total purchase price paid on all taxable items or services on the bill or invoice. If you sell only taxable items or services, the entire invoice amount is the amount subject to sales tax. If you sell a combination of taxable and nontaxable goods and services, you must identify which of the items are taxable and which are not. You must separately state the total amount of sales tax due on any receipt or invoice that you give to your customer.