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	$159.85	9.623%	$175.2324	$175.23	$175.25	$175.20
Purchase #2	$64.90	3.400%	$67.1066	$67.11	$67.10	$67.10
Purchase #3	$125.31	11.189%	$139.3309	$139.33	$139.35	$139.30
Purchase #4	$234.39	12.733%	$264.2349	$264.23	$264.25	$264.20
Purchase #5	$151.60	13.545%	$172.1342	$172.13	$172.15	$172.10
Purchase #6	$59.47	10.402%	$65.6561	$65.66	$65.65	$65.70
Purchase #7	$118.49	3.152%	$122.2248	$122.22	$122.20	$122.20
7 purchase totals =	$914.01		$1,005.9199	$1,005.91	$1,005.95	$1,005.80