Though Americans spend about $66 billion on tips each year, we rarely pause to consider the implications – or the effectiveness – of forking over some green to curry favor, say thank you, or smooth over a mistake. Bottom line: "It's greasing the social wheels. . . . Tipping is a bribe, a payoff, and a charity all at once," says Steve Dublanica, who traveled the country to immerse himself in our tipping culture for his book, 'Keep the Change,' in an attempt to become a "guru of the gratuity." Basing his recommendations on nine years in the service industry and 12 months interviewing everyone from pizza boys to prostitutes, Dublanica explains when to spend more, when to skimp, and when to pay it forward.