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	$44.47	6.792%	$47.4904	$47.49	$47.50	$47.50
Purchase #2	$38.34	4.435%	$40.0404	$40.04	$40.05	$40.00
Purchase #3	$208.95	11.584%	$233.1548	$233.15	$233.15	$233.20
Purchase #4	$84.94	5.249%	$89.3985	$89.40	$89.40	$89.40
Purchase #5	$238.45	7.835%	$257.1326	$257.13	$257.15	$257.10
Purchase #6	$155.57	12.570%	$175.1251	$175.13	$175.15	$175.10
Purchase #7	$143.67	5.255%	$151.2199	$151.22	$151.20	$151.20
7 purchase totals =	$914.39		$993.5617	$993.56	$993.60	$993.50