Yes, I do not what it is and how it works. Here is what I found when I researched this prior to answering you:
Groupon (a portmanteau derived from "group coupon") is a deal-of-the-day website that features discounted gift certificates usable at local or national companies. Groupon was launched on November 2008, the first market for Groupon was Chicago, followed soon thereafter by Boston, New York City, and Toronto. As of October 2010[update], Groupon serves more than 150 markets in North America and 100 markets in Europe, Asia and South America and has amassed 35 million registered users.
The idea for Groupon was created by now-CEO and Pittsburgh native Andrew Mason. The idea subsequently gained the attention of his former employer, Eric Lefkofsky, who provided $1 million in "seed money" to develop the idea. In April 2010, the company was valued at $1.35 billion. According to a report conducted by Groupon's marketing association and reported in Forbes Magazine, which was reported by the Wall Street Journal, Groupon is "projecting that the company is on pace to make $1 billion in sales faster than any other business, ever".
Groupon also owns several international operations, all of which were originally deal-of-the-day services similar to it, but then re-branded under the Groupon name after acquisition; these have included the European-based MyCityDeal (17 May 2010), the South American ClanDescuento (22 June 2010), the Singaporean Beeconomic.com, the Japanese service Qpod.jp, Russian Darberry.ru (both on 17 August 2010). Groupon has recently bought the Indian deal-of-the-day website SoSasta.com and will be re-branding it soon as well. The Groupon acquisitions of uBuyiBuy launched services under the Groupon name in Hong Kong, Singapore, the Philippines and Taiwan. Groupon also acquired GroupsMore.com in Malaysia to expand its business there. Prior to these acquisitions, Groupon had bought out the mobile technology company Mob.ly. Groupon is preparing for a $25 billion IPO in 2011. The Point, Inc., the predecessor to Groupon, bought the trademark "GROUP-ONS" from its originator in February 2009 under terms which allows the originator and first registrant of the trademark to continue the use of this trademark. In June 2011, Groupon filed with the SEC to raise up to $750 million in an initial public offering.[
By recording this as though it was a gift certificate you are taking into account the discount you are offering the customer.