While tipping rates vary by the type of service provided, by the region of the country and other factors, tipping 15-20% of the total bill is normal. For a 140.00 restaurant bill, you can leave $21 to $28.
Here's a general tipping guide shared by Emily Post Institute: 15% to 20% for sit-down restaurant service, 10% for servers at buffets (for help with drink orders and plate removal) and $1 to $2 per drink for bartenders, or 15% to 20% of the bar tab.
For valets ($2 to $5 to retrieve a vehicle), 15% to 20% for taxi drivers, hair stylists, and manicurists, and at least a couple of dollars for pizza delivery. For skycaps and hotel bellhops, figure on $2 for the first bag and $1 for each additional one. Doormen could receive a dollar or two to carry luggage or hail cabs.
For hotel staff, the institute suggests $2 to $5 per night, with money left each day (since housekeeping crews change throughout the week) and a thank-you note for the staff. Leave more if the room looks as if a hurricane went through it.
As for cash-register coin jars, there's no obligation to add money to them, although it might be worth it if you receive super service or you're a regular customer, the institute suggests.
See expert's guide to tipping in the United States featured at CNN.com.