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	$105.53	5.663%	$111.5062	$111.51	$111.50	$111.50
Purchase #2	$53.95	9.348%	$58.9932	$58.99	$59.00	$59.00
Purchase #3	$90.45	10.187%	$99.6641	$99.66	$99.65	$99.70
Purchase #4	$222.37	11.363%	$247.6379	$247.64	$247.65	$247.60
Purchase #5	$245.47	3.524%	$254.1204	$254.12	$254.10	$254.10
Purchase #6	$234.34	10.784%	$259.6112	$259.61	$259.60	$259.60
Purchase #7	$122.90	12.788%	$138.6165	$138.62	$138.60	$138.60
7 purchase totals =	$1,075.01		$1,170.1495	$1,170.15	$1,170.10	$1,170.10