Looking through questions tagged numeral-representations and questions tagged number-formats, I do see a difference: numeral-representations is almost exclusively about representations of integers (17/19 about integers, 2/19 about floating point), whereas number-formats is evenly spread (31/64 about floating point).
I definitely agree that we should have a single tag name to refer to representations of integers. But maybe we should have a different name for representations of floating point numbers? And what about other kinds of numbers (I could only find one question about exact arithmetic on rationals)?
Regarding the choice of primary tag name, it's usually a good idea to align with Wikipedia. If there's a debate to be had about naming, they've usually gone through it and we might as well not redo the debate here. Furthermore using the same terminology on major websites makes things easier to find for people. Wikipedia has an article “numeral system” about mathematical representations of integers, which is not exactly the same thing as representations inside computers, and an article “computer number format” which covers integers, exact non-integers and floating point.