Similar things have been suggested before, but since the rounding features are being reworked for Studiometry v12, I propose that a minimum charge feature be made available in the Billing Settings window of Preferences. As currently deployed in 11.2 and previous, there is a Rounding setting to round the timer result to the nearest hour or fraction of hour determined by a list box selection. There is also an option check box to Always round up.
This proposal is that an additional minimum charge selection be provided to round up to the first increment selected in the Rounding list box, and thereafter round to the nearest rounding increment selected.
For example, assume Quarter of an Hour is selected in the Rounding list box. If the timer accumulates 6 minutes for a task, the result would be rounded up to 15 minutes. If the timer accumulates 22 minutes, the result would be rounded down to 15 minutes. If the timer accumulates 22.5 or more minutes the result would be rounded up to 30 minutes.