Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.38	12.753%	$39.892	$39.89	$39.90	$39.90
Purchase #2	$77.41	5.269%	$81.4887	$81.49	$81.50	$81.50
Purchase #3	$192.51	8.161%	$208.2207	$208.22	$208.20	$208.20
Purchase #4	$10.39	10.733%	$11.5052	$11.51	$11.50	$11.50
Purchase #5	$19.35	4.727%	$20.2647	$20.26	$20.25	$20.30
Purchase #6	$51.39	9.771%	$56.4113	$56.41	$56.40	$56.40
Purchase #7	$213.94	7.721%	$230.4583	$230.46	$230.45	$230.50
7 purchase totals =	$600.37		$648.2409	$648.24	$648.20	$648.30