Yes, I was taught at school never to use the comma before the final 'and' as well, but as you say, it doesn't seem to be a strict rule anymore. Some people use it and some people don't.
https://en.wikipedia.org/wiki/Serial_comma
When the need arises, I use this comma to avoid ambiguity and/or to make the text look neater. I no longer follow the rule about this comma that we were taught at school. It seems silly today not to use the comma when required, and as the Wikipedia article above shows, sometimes it is essential to use it to avoid misunderstandings.