How to round to next/previous 15 minutes?

`const now = dayjs(); // e.g. 'HH:mm' is 17:37`

But what I want to modify the object to snap to `17:30` or `17:45`.

Is there a way to do it? "Rounding" only seems to be a thing in relative time, which is not what I'm looking for.

Start by reviewing the existing Day.js APIs and documentation for unit manipulation and relative-time rounding. Determine how a value such as 17:37 should snap to the nearest 15-minute boundary, then verify that the resulting API or documented approach handles both previous and next boundaries.

Written by the indexing model from the issue text.