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	$63.58	4.651%	$66.5371	$66.54	$66.55	$66.50
Purchase #2	$213.80	12.176%	$239.8323	$239.83	$239.85	$239.80
Purchase #3	$100.75	7.693%	$108.5007	$108.50	$108.50	$108.50
Purchase #4	$100.88	10.339%	$111.31	$111.31	$111.30	$111.30
Purchase #5	$177.40	4.359%	$185.1329	$185.13	$185.15	$185.10
Purchase #6	$208.59	13.490%	$236.7288	$236.73	$236.75	$236.70
Purchase #7	$208.66	7.810%	$224.9563	$224.96	$224.95	$225.00
7 purchase totals =	$1,073.66		$1,172.9981	$1,173.00	$1,173.05	$1,172.90