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	$106.35	6.353%	$113.1064	$113.11	$113.10	$113.10
Purchase #2	$85.85	4.466%	$89.6841	$89.68	$89.70	$89.70
Purchase #3	$235.70	8.509%	$255.7557	$255.76	$255.75	$255.80
Purchase #4	$234.31	9.200%	$255.8665	$255.87	$255.85	$255.90
Purchase #5	$167.56	6.564%	$178.5586	$178.56	$178.55	$178.60
Purchase #6	$233.73	9.637%	$256.2546	$256.25	$256.25	$256.30
Purchase #7	$159.58	13.143%	$180.5536	$180.55	$180.55	$180.60
7 purchase totals =	$1,223.08		$1,329.7795	$1,329.78	$1,329.75	$1,330.00