The way to get rid of coins is to spend them. This goes for every currency. If you manage your wallet properly you should never have more than $20 of HKD coins, unless some cash-only shop runs out of the right change and offloads lots of coins onto you.

The majority of cash-only shops price things in whole dollars. So you should never really get any cents in change as you can usually pay by card or octopus where things are priced in cents, except the odd 50c very occasionally. You can just overpay for a bus / tram if you don't have the exact amount and want to dump some coins.

Any 7-11 or Circle K would be happy to accept $50 in coins to load an Octopus. I have done it with $50 in 50c. The guy just pressed the button for $50 and said he would count it later. You can only load Octopodes in multiples of $50 so it doesn't help with getting rid of odd amounts.

If you happen to be in the area where the government's coin cart is located that week, you can load any amount of coins onto an Octopus. But the security guard will go through all the coins before putting them in a machine and will give you back anything which is dirty/stained/bent etc., which you are now unable to spend because people will notice and reject them, whereas if you spent one damaged coin alongside a lot of normal coins nobody would care.

During working hours, you can go to the basement of HSBC Headquarters in Central, or the basement of HSBC Building, 673 Nathan Rd, Mong Kok (next to MTR / corner of Argyle St). Those are the public cash services counters where you can exchange up to 500 coins to notes for free and also notes to other notes. They also exchange old coins, i.e. the 10-sided $5, big $1, silver 50c, big 10c and 5c. This service is meant to be free to HSBC customers only, but they don't even have computers there so cannot verify. They charge 2% for more than 500 coins (1% if you flash a card with an HSBC logo on it).


MOP is not a useless currency because it represents a 2.9% discount over HKD. If you decide to use HKD cash in Macau, you shouldn't ever touch any MOP because they give change in HKD. The only place I have found in Macau that returns MOP change even if you pay HKD is the HZMB shuttle bus counter. But they accept cards there so the problem shouldn't arise.

Anyway, MOP coins are not a problem because you can change exact amounts back to HKD at a currency exchange.