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	$137.72	7.719%	$148.3506	$148.35	$148.35	$148.40
Purchase #2	$49.85	5.854%	$52.7682	$52.77	$52.75	$52.80
Purchase #3	$131.92	11.350%	$146.8929	$146.89	$146.90	$146.90
Purchase #4	$20.77	11.866%	$23.2346	$23.23	$23.25	$23.20
Purchase #5	$177.47	6.508%	$189.0197	$189.02	$189.00	$189.00
Purchase #6	$152.69	13.518%	$173.3306	$173.33	$173.35	$173.30
Purchase #7	$250.78	9.733%	$275.1884	$275.19	$275.20	$275.20
7 purchase totals =	$921.20		$1,008.7850	$1,008.78	$1,008.80	$1,008.80