Your post sent me searching for the Graybar catalog that I have here, as I remember seeing a xfmr section in it, mostly Square D dry types.

I notice that several with 480V primaries specify 2.5% taps, 2 above and 4 below nominal 480.

I see as well that there is a range of single-phase types up to 100kVa or more with a 120/240 secondary and a 240/480 primary. I assume this is so the same version can be hooked-up to a 277/480 Y or a 240 delta supply?

We don't have such an arrangement of different supply systems here. 240/415V Y is the standard LV; if the load is too great for the PoCo to supply at LV, then they get 11kV delta (or 33kV delta if it's a really big place).