A recent news story (here or here [SCMP, gated]) discusses the right to spend pennies in the United States:
A group of people this month protested in front of a Chinese takeaway restaurant in the Bronx after a customer said the cashier refused to accept 10 pennies as part of the payment for a US$2.75 dish. [....]
"This is America. If you want to do business in America, you have to accept all American currency," said Ruben Diaz, the Democratic senator who attended the protest.
The Senator is correct. In the United States, all US currency is "legal tender." That means that it must be accepted by law in exchange for a debt. Senator Diaz wants to enforce this law, with a threat of a $500 fine for any retailer who refuses to be paid in pennies!
This is absurd. Imagine buying a new car, and insisting on paying with pennies. Just counting, storing, securing, and exchanging the pennies into more useful currency would probably cost the car dealer more than the $500 fine. But that's the law... in the US at least.
In most countries, a more reasonable approach is taken. Money and Legal Tender are not identical. Take, for example, this quote from the Bank of Canada website:
The method of payment can be whatever is mutually acceptable to both parties — cash, credit card, cheque, etc. Thus, a merchant may refuse to accept bank notes in payment for goods or services, without contravening the law.
Other countries define in law what is reasonable for a retailer to accept, and enforce those standards. For example, in the United Kingdom,
... only coins valued 1 pound Sterling and 2 pounds Sterling are legal tender in unlimited amounts throughout the territory of the United Kingdom. [...]
Currently, 20 pence pieces and 50 pence pieces are legal tender in amounts up to 10 pounds; 5 pence pieces and 10 pence pieces are legal tender in amounts up to 5 pounds; and 1 penny pieces and 2 pence pieces are legal tender in amounts up to 20 pence.
This Wikipedia site contains the rules for many other countries.
What about Hong Kong? A quick search on the web didn't show up any results, although some stores openly advertise that they do not accept $1000HKD notes, and taxi drivers are not obliged to accept $500HKD notes as well.
As the SCMP article suggests, if you have to pay a fine in the US, insist on paying it in pennies. You would be fully within your rights to do so! In any other country, just be reasonable....