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	$59.47	9.747%	$65.2665	$65.27	$65.25	$65.30
Purchase #2	$130.85	11.485%	$145.8781	$145.88	$145.90	$145.90
Purchase #3	$43.89	7.429%	$47.1506	$47.15	$47.15	$47.20
Purchase #4	$184.52	6.403%	$196.3348	$196.33	$196.35	$196.30
Purchase #5	$215.50	10.733%	$238.6296	$238.63	$238.65	$238.60
Purchase #6	$157.85	4.574%	$165.0701	$165.07	$165.05	$165.10
Purchase #7	$8.64	12.859%	$9.751	$9.75	$9.75	$9.80
7 purchase totals =	$800.72		$868.0807	$868.08	$868.10	$868.20