Not sure what to give the babysitter, dog walker or house-cleaner this holiday season? Here's a guide.

DURING THE HOLIDAYS, certain perplexing questions trouble even the sharpest of minds, like "How is Santa able to deliver so many toys in one night?" And: "How much am I supposed to tip the newspaper boy again?"

While the first question remains one of life's great mysteries, we went to etiquette expert Peggy Post — granddaughter-in-law of manners maven Emily Post — for tips on holiday tipping. Post ought to know: She currently writes the etiquette column for Good Housekeeping and helps run the Emily Post Institute, an organization dedicated to the art of politeness.

But when it comes to the baffling issue of whom to tip and how much, even Post admits the rules aren't black and white. "These are really relationships questions where there is no right or wrong," she says. "The basic thing about holiday tipping is that it's a custom in our culture to thank those who regularly serve us throughout the year."

Post says determining what's a suitable tip depends on the frequency and the quality of the service provided. Obviously, if you find the service inadequate or expect to discontinue it, no tip is required. But for those who do help make your life a bit better throughout the year, here are some guidelines to help determine what gesture is appropriate:

The Tip Sheet
Who should be on your holiday tip list? Start with those you probably can't fathom life without, namely a nanny (or babysitter) and housecleaner. These folks are entrusted with your most valuable things — your children and your homes. Keeping them happy should be a top priority. And considering how hard it is to find someone you like, this is no time to be stingy. (For dollar specifics, see the table on the right.)

You may also want to tip the "regulars" in your life, like your hairdresser, fitness trainer and parking lot attendants. That said, if you've been tipping generously throughout the year, this may not be necessary. "If you've been tipping someone regularly at time of service, you don't have to at the end of the year — but most do," says Post. "You could tone back if you tip every time."

Keep in mind that most salon owners and other small business owners don't accept tips. These people are rewarded by your patronage.

Tipping Points
Once you know who's on your tip list, you must figure out who gets what. We cynics are inspired to give generously not as a heartfelt thank-you for services rendered over the past year, but rather as a bribe for continued good service in the year to come. There actually may be some precedent to this: Many historians trace tipping to 16th century English pubs, where patrons desiring quick service would place a coin in a box inscribed TIP for "To Insure Promptness."

"Many people think, 'What choice do I have? If I don't tip they'll think I'm a bad guy and they won't take care of me,'" says Post. "A lot of people feel really put out by this, but most of these people in the service business rely on tips for their income. It's part of our culture." In other words, in many cases you should simply view the tip as part of the bill for service. Choose to ignore it, and you could see a lot of your newspapers carefully delivered to that puddle in the driveway.

Just what tip amount is appropriate depends on where you live (suburban, urban or rural) and local customs. In some cases, a cash gift is not advised. For instance, cash is not an appropriate gift for a teacher, since this could look like a bribe. Also, before you buy a gift individually, check with the school's policy. Sometimes the class parents will join together to purchase a gift together or contribute supplies to the classroom. Post also advises not to give your boss an individual gift, since this can look like a shameless ploy to win favor. A group gift is the better way to go.

You should also be sure to check on the policy for tipping local municipal employees as many municipalities don't allow tips. U.S. Postal Service regulations allow employees to accept gifts worth up to $20.