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	$7.60	11.191%	$8.4505	$8.45	$8.45	$8.50
Purchase #2	$53.37	4.531%	$55.7882	$55.79	$55.80	$55.80
Purchase #3	$195.46	6.782%	$208.7161	$208.72	$208.70	$208.70
Purchase #4	$240.57	10.867%	$266.7127	$266.71	$266.70	$266.70
Purchase #5	$88.50	3.677%	$91.7541	$91.75	$91.75	$91.80
Purchase #6	$105.45	5.640%	$111.3974	$111.40	$111.40	$111.40
Purchase #7	$95.58	4.420%	$99.8046	$99.80	$99.80	$99.80
7 purchase totals =	$786.53		$842.6236	$842.62	$842.60	$842.70