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	$70.76	11.396%	$78.8238	$78.82	$78.80	$78.80
Purchase #2	$56.83	3.244%	$58.6736	$58.67	$58.65	$58.70
Purchase #3	$166.70	3.254%	$172.1244	$172.12	$172.10	$172.10
Purchase #4	$11.63	10.663%	$12.8701	$12.87	$12.85	$12.90
Purchase #5	$61.83	5.671%	$65.3364	$65.34	$65.35	$65.30
Purchase #6	$66.69	11.422%	$74.3073	$74.31	$74.30	$74.30
Purchase #7	$55.41	13.293%	$62.7757	$62.78	$62.80	$62.80
7 purchase totals =	$489.85		$524.9113	$524.91	$524.85	$524.90