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	$134.77	5.626%	$142.3522	$142.35	$142.35	$142.40
Purchase #2	$190.44	10.548%	$210.5276	$210.53	$210.55	$210.50
Purchase #3	$85.66	4.602%	$89.6021	$89.60	$89.60	$89.60
Purchase #4	$108.66	11.439%	$121.0896	$121.09	$121.10	$121.10
Purchase #5	$40.27	5.739%	$42.5811	$42.58	$42.60	$42.60
Purchase #6	$58.33	11.147%	$64.832	$64.83	$64.85	$64.80
Purchase #7	$11.77	8.421%	$12.7612	$12.76	$12.75	$12.80
7 purchase totals =	$629.90		$683.7458	$683.74	$683.80	$683.80