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	$111.30	8.104%	$120.3198	$120.32	$120.30	$120.30
Purchase #2	$247.76	5.191%	$260.6212	$260.62	$260.60	$260.60
Purchase #3	$46.49	9.213%	$50.7731	$50.77	$50.75	$50.80
Purchase #4	$146.43	7.366%	$157.216	$157.22	$157.20	$157.20
Purchase #5	$199.49	11.588%	$222.6069	$222.61	$222.60	$222.60
Purchase #6	$175.27	7.419%	$188.2733	$188.27	$188.25	$188.30
Purchase #7	$80.47	6.808%	$85.9484	$85.95	$85.95	$85.90
7 purchase totals =	$1,007.21		$1,085.7587	$1,085.76	$1,085.65	$1,085.70