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	$89.70	12.209%	$100.6515	$100.65	$100.65	$100.70
Purchase #2	$49.82	9.729%	$54.667	$54.67	$54.65	$54.70
Purchase #3	$132.78	4.851%	$139.2212	$139.22	$139.20	$139.20
Purchase #4	$169.83	7.413%	$182.4195	$182.42	$182.40	$182.40
Purchase #5	$45.86	8.253%	$49.6448	$49.64	$49.65	$49.60
Purchase #6	$12.28	10.768%	$13.6023	$13.60	$13.60	$13.60
Purchase #7	$157.48	9.657%	$172.6878	$172.69	$172.70	$172.70
7 purchase totals =	$657.75		$712.8941	$712.89	$712.85	$712.90