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	$231.32	12.142%	$259.4069	$259.41	$259.40	$259.40
Purchase #2	$177.58	10.760%	$196.6876	$196.69	$196.70	$196.70
Purchase #3	$141.90	6.874%	$151.6542	$151.65	$151.65	$151.70
Purchase #4	$190.28	3.149%	$196.2719	$196.27	$196.25	$196.30
Purchase #5	$158.51	11.656%	$176.9859	$176.99	$177.00	$177.00
Purchase #6	$23.81	12.686%	$26.8305	$26.83	$26.85	$26.80
Purchase #7	$183.52	4.210%	$191.2462	$191.25	$191.25	$191.20
7 purchase totals =	$1,106.92		$1,199.0832	$1,199.09	$1,199.10	$1,199.10