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	$33.66	5.539%	$35.5244	$35.52	$35.50	$35.50
Purchase #2	$249.70	6.365%	$265.5934	$265.59	$265.60	$265.60
Purchase #3	$94.76	10.628%	$104.8311	$104.83	$104.85	$104.80
Purchase #4	$155.57	11.699%	$173.7701	$173.77	$173.75	$173.80
Purchase #5	$112.55	3.476%	$116.4622	$116.46	$116.45	$116.50
Purchase #6	$14.96	5.422%	$15.7711	$15.77	$15.75	$15.80
Purchase #7	$58.27	3.399%	$60.2506	$60.25	$60.25	$60.30
7 purchase totals =	$719.47		$772.2029	$772.19	$772.15	$772.30