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	$235.89	5.653%	$249.2249	$249.22	$249.20	$249.20
Purchase #2	$249.71	3.509%	$258.4723	$258.47	$258.45	$258.50
Purchase #3	$54.67	10.677%	$60.5071	$60.51	$60.50	$60.50
Purchase #4	$142.86	7.816%	$154.0259	$154.03	$154.05	$154.00
Purchase #5	$116.77	12.646%	$131.5367	$131.54	$131.55	$131.50
Purchase #6	$10.72	12.866%	$12.0992	$12.10	$12.10	$12.10
Purchase #7	$160.68	7.529%	$172.7776	$172.78	$172.80	$172.80
7 purchase totals =	$971.30		$1,038.6437	$1,038.65	$1,038.65	$1,038.60