No sales tax is charged when a person buys a gift card. Sales tax is imposed later when the gift card is used to buy a taxable good or service, but no tax if the card bought groceries or other tax-exempt goods.
In the landmark case of Petition of HDV Manhattan LLC [pdf], the Hustler Club in New York City (located at 51st Street and 12th Avenue) sold to patrons 'scrip' known as Beaver Bucks. Beaver Bucks was used for certain purchases within the Club, such as admission to private rooms, lap dances, and tips.
A 20% surcharge is imposed on each purchase of Beaver Bucks. For example, $100 of Beaver Bucks would require a $120 charge to the patron's credit card, from a company called Reading to Blind African Children LLC or a similar name.
Club employees would redeem their Beaver Bucks at the end of each work day, with different redemption rates for different employees. The Club sells around $1 million Beaver Bucks each month.
Unfortunately for the Club, its management could not prove how much of the Beaver Bucks was used for sales-taxable services such as lap dancing, and how much was used for sales-tax-exempt purchases. The court therefore concluded that all $24 million of Beaver Bucks sold in 2006-2008 should have been subject to the 8.875% New York sales tax.
The obvious solution is for the Club to provide all of its entertainers and hosts with sales tax calculators and receipt generators, so that each private dance purchase for $120 (according to the Internet) would require an extra $10.65 in Beaver Bucks for taxes.