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	$147.76	8.185%	$159.8542	$159.85	$159.85	$159.90
Purchase #2	$121.35	13.733%	$138.015	$138.02	$138.00	$138.00
Purchase #3	$225.32	13.798%	$256.4097	$256.41	$256.40	$256.40
Purchase #4	$18.28	5.287%	$19.2465	$19.25	$19.25	$19.20
Purchase #5	$99.88	13.247%	$113.1111	$113.11	$113.10	$113.10
Purchase #6	$204.91	13.778%	$233.1425	$233.14	$233.15	$233.10
Purchase #7	$18.88	12.111%	$21.1666	$21.17	$21.15	$21.20
7 purchase totals =	$836.38		$940.9456	$940.95	$940.90	$940.90