N'importe quoi is a very peculiar expression in French.
N'importe quoi = "anything"
The original meaning of n'importe quoi is "anything", but it's not the most common use of it.
(main meaning) N'importe quoi = "nonsense"
It is most commonly used to express a lack of understanding at a situation. It is actually closer to "nonsense".
It is a very difficult expression to translate to English, as it can be translated differently depending on the context.
Note that 'n'importe quoi' is a very common expression.
See also the related lesson: Autre chose / quelque chose d'autre = Something else (indefinite pronouns)
Learn more about these related French grammar topics
Examples and resources
Q&A Forum 2 questions, 5 answers
N'importe quoi and regarde-le pronunciation.
Wow! Such an interesting question!
The fact is that I had never really noticed these cases where indeed we do pronounce the final e [euh]. This isn't a regional particularity here, as we would all do it :)
The only explanation I can give relates to poetry reading:
In poetry, if the mute "e" at the end of a word is followed by a consonant (la belle robe), you will need to pronounce it to respect the pace of the poem.
In those cases, I think a similar rule applies, to make it sound more harmonious to the French ear.
Some people speaking fast could omit them, but doing so immediately sounds less elegant.
I hope that's helpful!
Bonne journée !