What I meant to imply was that the emergence of fractional dollar tick sizes was probably due to the fact that they were easier to deal with before the advent o

What I meant to imply was that the emergence of fractional dollar tick sizes was probably due to the fact that they were easier to deal with before the advent of computerized execution, clearing, and settlement. By the mid nineties most of that had been automated and there was therefore no good reason for such large tick sizes. When humans were still doing all trade processing manually, it made sense to have a system that incentivized fewer large trades (vs more smaller trades). Large minimum price variations and round lot requirements would have been a means to that end.