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	$102.37	3.118%	$105.5619	$105.56	$105.55	$105.60
Purchase #2	$24.85	11.676%	$27.7515	$27.75	$27.75	$27.80
Purchase #3	$69.95	3.152%	$72.1548	$72.15	$72.15	$72.20
Purchase #4	$21.45	10.824%	$23.7717	$23.77	$23.75	$23.80
Purchase #5	$38.80	4.662%	$40.6089	$40.61	$40.60	$40.60
Purchase #6	$173.51	8.662%	$188.5394	$188.54	$188.55	$188.50
Purchase #7	$31.37	10.534%	$34.6745	$34.67	$34.65	$34.70
7 purchase totals =	$462.30		$493.0627	$493.05	$493.00	$493.20