If you set up a rounding rule on a leave type and add it to a plan with 'Accrual policy on enrolment' set to Prorated, the rounding rule is observed when enrolling a worker part way through an Accrual period. If the tier on the plan has 'Use full time equivalency' ticked the rounding rule is ignored.

If customers have specified that they want accrued balance to be rounded and accruals are then generated that don't observe those settings, they rightly feel that the functionality isn't behaving correctly.