Add this to the rising cost of the gift-giving season: holiday tips are up about $5 apiece, and the list of tippees is growing.

That's according to Consumer Reports National Research Center, which surveyed 1,800 people on what gratuities they gave last year.

The results showed a $5 increase per tip compared to the year before. In addition, the usual recipients -- hairdressers, newspaper carriers, house cleaners and child-care providers -- are joined now by fitness trainers, spa attendants, dog walkers and elder-care workers.

In the December issue of Consumer Reports magazine, Michael Lynn, associate professor of consumer behavior at Cornell University, says that tipping habits are regional: People in the Northeast tip the most while Southerners tip the least.

That, etiquette expert Colleen Rickenbacker of Dallas tells the magazine, is because Southerners often tip with homemade gifts in addition to, or instead of, money.

The magazine offers the following tipping etiquette:

• When in doubt, give the equivalent of one week's pay or one session.

• Be careful with gift cards; they often go unclaimed. And avoid bank-issued cards, which often have fees and expiration dates.

• Know the employer's rules. Mail carriers aren't supposed to accept cash or gift cards that can be exchanged for cash. Tipping teachers can be seen as a bribe, so try movie-ticket coupons or a gift certificate given jointly with other parents.

• No limp paper. If giving cash, use fresh new bills with a thank-you note.

According to the Emily Post Institute, whether and how much to tip depends on the following criteria: quality and frequency of service, relationship with the provider, how long you've known each other, where you live (amounts in big cities are usually higher), your budget, regional customs and type of establishment (deluxe vs. moderate).