Please help me to communicate better the opinion of the speaker in these two cases:

Worker: - Boss, we have spend 200 euro more in Facebook advertisments this month.
Director: - Don't worry about this. This is nothing. (This is not important / We shouldn't concern about this this thing).
(i.e. The advertisement budget of the company is 5,000 per month. The director consider this amount as trivial)

My translation will be: - Это мелочь
My question is, can I also use plural: - Это мелочи

Worker: - Boss, we should first write a report to public authorities before starting the applications.
Director: - These are details!
(i.e. The director does not consider that this action is important).

Man flirting with an unknown woman: - Do you want to go for a coffee
Woman: - I am married
Man: - Details.
(i.e. The man is trying to impress by saying that he does not care about her marital statues he just want to flirt with her).