Not sure what you mean by tapered or sword. Warding files have two large flat surfaces that are parallel planes i.e. the thickness between the two flats doesn't taper. They make slits or slots with parallel sides. The other two surfaces (the thin ones) are not usually parallel, so there's some taper with the tip of the file being smaller in that dimension.

I think the name warding comes from the warding grooves in a key to a lock. Imagine having to file that groove — you need the sides of the groove to be parallel.