All of your blocks are going to measure the same (unfinished) size for this quilt. So when you round up to the 5" for the HST pieces when you sew/cut/press you'll be a tad over the 4.5". In theory if you did the 4 7/8 cut and cut and sewed accurately, your finished HST will be 4.5". So doing the 5" initial cut will give you a smidge over the 4.5 (unfinished) square. You can then trim to the 4.5". I like putting the 45 deg. line on my ruler on the diagonal sewn line and trim from there to the correct finished size. For me it makes for a really accurate HST and everything then matches up correctly.