Summary

These are the minimum improvements I mentioned in the issue below + some interpolated strings in the code snippet. I would personally be fine with this version of the doc, but there could still be some additions:

• Add directed modes to the snippet. I decided to leave this one out for now because the snippet is already kind of big, and it would duplicate information already in the "Directed rounding" table.
• It is not immediately clear that "precision" in the doc's context means "number of decimal places", but I guess there is a reason it's written this way. For reference, the parameter name on Math.Round correctly mentions "fractional digits". This is confusing because, to me at least, "precision" == "number of significant (not fractional) digits".
• The explanation for the rounding to nearest modes is quite long, but I did not want to shorten without some feedback if this is even desirable (the "for" argument could be that it makes the reader "drown in letters", the "against" is that clarity > brevity).

Should I add anything from the above?

Fixes dotnet/docs#19314
cc @gewarren