It's not really a matter of rounding of pages in the usual sense. Yes, round up, but not to the nearest page, to the nearest 16 pages! You cannot print fewer than 16 pages (one signature) at a time.
C(p) = .14 * Ceiling(p/16), where "Ceiling(x)" is the nearest integer greater than or equal to x.
Ceiling(4) = 4
Ceiling(5.2) = 6
etc.