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	$35.68	13.206%	$40.3919	$40.39	$40.40	$40.40
Purchase #2	$122.97	10.322%	$135.663	$135.66	$135.65	$135.70
Purchase #3	$42.74	5.509%	$45.0945	$45.09	$45.10	$45.10
Purchase #4	$58.47	12.431%	$65.7384	$65.74	$65.75	$65.70
Purchase #5	$63.36	5.748%	$67.0019	$67.00	$67.00	$67.00
Purchase #6	$52.58	13.459%	$59.6567	$59.66	$59.65	$59.70
Purchase #7	$116.35	13.376%	$131.913	$131.91	$131.90	$131.90
7 purchase totals =	$492.15		$545.4594	$545.45	$545.45	$545.50