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	$25.70	10.684%	$28.4458	$28.45	$28.45	$28.40
Purchase #2	$35.65	13.813%	$40.5743	$40.57	$40.55	$40.60
Purchase #3	$85.88	5.443%	$90.5544	$90.55	$90.55	$90.60
Purchase #4	$63.52	9.581%	$69.6059	$69.61	$69.60	$69.60
Purchase #5	$229.81	6.185%	$244.0237	$244.02	$244.00	$244.00
Purchase #6	$5.66	13.260%	$6.4105	$6.41	$6.40	$6.40
Purchase #7	$163.35	6.225%	$173.5185	$173.52	$173.50	$173.50
7 purchase totals =	$609.57		$653.1331	$653.13	$653.05	$653.10