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	$56.55	8.149%	$61.1583	$61.16	$61.15	$61.20
Purchase #2	$133.54	9.626%	$146.3946	$146.39	$146.40	$146.40
Purchase #3	$19.43	8.519%	$21.0852	$21.09	$21.10	$21.10
Purchase #4	$56.37	4.628%	$58.9788	$58.98	$59.00	$59.00
Purchase #5	$166.40	3.388%	$172.0376	$172.04	$172.05	$172.00
Purchase #6	$125.79	12.502%	$141.5163	$141.52	$141.50	$141.50
Purchase #7	$141.28	3.832%	$146.6938	$146.69	$146.70	$146.70
7 purchase totals =	$699.36		$747.8646	$747.87	$747.90	$747.90