sounds like an episode from The Clash Of the Titanic Egos!!
honestly bro when you insist on him giving you 0.5 change you descend to his level ...
and you're lucky he had change for the 500, (I'm pretty sure) he's only legally required to carry change for 100 ...
Yes, it is normal protocol in Hong Kong to round up the fare. May seem strange, but it is HK Chinese culture. Just as there are no tips, remember, it is also normal to leave some small change on the table at a restaurant, and to round up the fare in a taxi.
Taxi drivers all over the world are in the job for the money not for the good company. And given that HK taxi drivers are mostly excellent - I've had very few situations that raised my blood pressure. I have had many situations where the driver rounded down - but I have to say they were not the minimum fare.
At the end of the day, the meter is there to protect you
and to protect him!