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	$33.88	8.131%	$36.6348	$36.63	$36.65	$36.60
Purchase #2	$54.68	12.734%	$61.643	$61.64	$61.65	$61.60
Purchase #3	$36.33	11.468%	$40.4963	$40.50	$40.50	$40.50
Purchase #4	$99.38	5.234%	$104.5815	$104.58	$104.60	$104.60
Purchase #5	$166.49	6.624%	$177.5183	$177.52	$177.50	$177.50
Purchase #6	$106.27	9.626%	$116.4996	$116.50	$116.50	$116.50
Purchase #7	$62.72	12.532%	$70.5801	$70.58	$70.60	$70.60
7 purchase totals =	$559.75		$607.9536	$607.95	$608.00	$607.90