restaurants and hotels automatically tag on to the bill a 10% service charge (as
you would read on the menu, often in fine print). But it's accepted practice to still give a little beyond that, typically by leaving the loose change under 5 or 10 dollars.
Small eating places such as 'cha chaan tang' ('tea restaurants') may not have a 10% charge, typically in those where you have to walk to the cashier yourself to pay. But tipping by leaving a few coins is
till accepted practice.
Tipping taxi drivers by rounding the fare off to tens (dollars) is fairly common when it's just a dollar or two tip. Tipping more than that will get you a nice word of thanks. And beware that taxi drivers routinely just round it up to the whole dollar.
One place that you might want to get prepared with some
coins to tip is the hotel bathroom. Not the one in your own room, thankfully.
In bigger hotels, there is an attendant there to attend to your needs - hand you a
towel or even a comb. It is a dirty job, but someone wants to do it!
Hong Kong is all about efficiency. Nowadays many restaurants have a practice with making change after you pay that may catch you by surprise. It goes like this. The waiter brings your bill in a small open folder. You put the money on it. In a flash, when you look back, your cash has magically changed into smaller bills and coins! I've seen a tourist taken aback and ask, "What have you done with my money?" Actually, the folder has more than one fold. The other fold(s) is already pre-loaded with the correct change in anticipation of the amount you'll pay. With a flip of his hand, the waiter shows you the change. Slick, huh?!