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	$99.77	8.518%	$108.2684	$108.27	$108.25	$108.30
Purchase #2	$160.52	11.770%	$179.4132	$179.41	$179.40	$179.40
Purchase #3	$175.52	10.603%	$194.1304	$194.13	$194.15	$194.10
Purchase #4	$38.77	4.117%	$40.3662	$40.37	$40.35	$40.40
Purchase #5	$24.58	13.544%	$27.9091	$27.91	$27.90	$27.90
Purchase #6	$250.73	11.432%	$279.3935	$279.39	$279.40	$279.40
Purchase #7	$191.68	6.450%	$204.0434	$204.04	$204.05	$204.00
7 purchase totals =	$941.57		$1,033.5242	$1,033.52	$1,033.50	$1,033.50