If you cut the squares to 2.25 (2-1/4) and sewed them with a full quarter inch seam (versus a scant quarter inch seam) you might end up with a piece really close to 5.5 inches (unfinished size)
If it's only a smidge oversized, I think it would be feasible to trim the blocks down to the desired sze.
The technical size to cut the squares would be 2-1/6 inches - which most rulers don't have.
1/6 = 0.167
3/16 = 0.189
1/4 = 0.25