When I played 6/12 the sb was $3. Players without ones would post two chips and the dealer would break one to return change to the small blind if he folds.
I would guess the rationale is it's not a big deal to the dealer because they still rake to the nearest dollar so breaking twos into singles is pretty common anyway.
On the other hand when they spread 15/30 with fives, they do let the SB stay at 10. I presume because unless they make change to 7.50 it's going to be imperfect anyway. Also they do not use 50 cent chips in the rake, and besides that game would almost always generate max rake. (I believe the rake was 1 for every 30 up to 4 when that game was active.)