Traveling is supposed to be relaxing, but many feel their chest tighten when they encounter multiple tipping opportunities: cab drivers, bellhops, doormen. Do you tip them all? Do you tip them all the same amount? How do you know?

See also: Protect yourself from these 5 diseases when traveling abroad.

To help Americans better understand appropriate gratuities, Angie's List, a consumer website for rating service professionals, surveyed members and service professionals to get their take on American tipping protocol. (The latter's unsurprising consensus: When in doubt, tip big!)

Here are our tips for domestic travel tipping:

Hotel Tipping

Bellhop: $1 to $2 per bag

Car valets: $1 to $3. You can tip when you drop off the car if you like, but definitely tip at pickup.

Room service: 10 percent is acceptable, 15 percent to 20 percent for a large or difficult order.

Housekeeping: $2 to $3 per night; $5 if you have more than three people in a room/suite. Leave the money in an envelope with "Thank You" on it, so they know the money is for them.

Concierge: Nothing. But if you have something brought to your room, such as a sewing kit or extra toothbrush, a $2 to $3 tip is appropriate.

Cabana attendant: 15 percent to 20 percent of your total bill

Tanning attendant: $5 to $10 per lotion application

Doorman: $1 for help with each bag, $1 for hailing a cab

Transportation Tipping

Cab driver: 15 percent to 20 percent tip of the fare. (Find out ahead of time if your cabbie accepts a credit card. If he or she doesn't, make sure you have enough cash for both fare and tip.)

Airport Red Cap/Baggage personnel: $1 to $2 per bag  
 
Wheelchair attendants: This really depends on the level of service. If the attendant is transporting the passenger from the check-in to the gate, $5 to $10 is the standard, especially if the attendant assists in helping the passenger from a car. If the attendant is also wrangling bags and with the passenger for a longer period of time, a $10 to $20 tip is appropriate, depending on the number of bags.
 
Airport transportation attendants: If the driver helps you with your bags, offer $1 per bag.

Next: What about tipping at restaurants? »