Both PCGS and NGC only require the respective bands to be clearly separated and free of marks or other issues which interfere with that separation. I have never seen a requirement that the bands be "rounded" -- perhaps it's a holdover from older grading systems. I looked at all of my certified FB dimes and out of the (admittedly very small) grouping, only one has the "rounded" look to the bands, and that's a MS67FB PCGS graded example. The others all look more or less like this 1938, some with slightly better definition and "depth" to the split.
I don't really mind if it's FB or not; it's not like I'm sending it out to get slabbed :) The discussion has been very educational, though, and it's interesting to see that what counts as FB vs. non-FB is more subjective than one might think at first glance.
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