Every ten point scale collapses into a two point scale within about a year. Nothing scores below seven, everything decent scores eight, and the good ones score nine, at which point the number is doing no work at all and you may as well print a tick.
Nine is deliberately awkward. It has a true middle at five, which means a five can be used without it reading as a failure, and it makes a six mean something specific rather than mean disappointing. Reserving the top mark for something that may never arrive keeps the eights honest.
Half marks are allowed. Quarter marks are not, because at that point the precision is invented.