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	$55.68	6.733%	$59.4289	$59.43	$59.45	$59.40
Purchase #2	$230.52	8.370%	$249.8145	$249.81	$249.80	$249.80
Purchase #3	$177.82	9.250%	$194.2684	$194.27	$194.25	$194.30
Purchase #4	$140.51	13.526%	$159.5154	$159.52	$159.50	$159.50
Purchase #5	$230.98	4.796%	$242.0578	$242.06	$242.05	$242.10
Purchase #6	$195.95	4.370%	$204.513	$204.51	$204.50	$204.50
Purchase #7	$6.39	11.426%	$7.1201	$7.12	$7.10	$7.10
7 purchase totals =	$1,037.85		$1,116.7181	$1,116.72	$1,116.65	$1,116.70