Thank you for being honest that this is for your manuscript. As such, I cannot give you a specific answer. But I can tell you some general things about headings. According to 4.2 in Braille Formats, "centered headings are used to represent the print headings of major sections of the text, and cell 5 and cell 7 headings are used to represent the print headings for subsections shown within major sections". There is no rule that says "this type of print MUST be this type of heading". It is up to the transcriber to determine, based on the material being transcribed, what is a major heading and what is a sub heading. I would suggest reading carefully through section 4 of Braille Formats for more information (and examples) on headings. Then decide how you will do your headings and be consistent.
As a side note, I'm doing a webinar on headings this Friday 🙂 1:00 Eastern. There is a blog about it on the website.