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	$37.99	12.815%	$42.8584	$42.86	$42.85	$42.90
Purchase #2	$11.87	6.153%	$12.6004	$12.60	$12.60	$12.60
Purchase #3	$54.57	5.738%	$57.7012	$57.70	$57.70	$57.70
Purchase #4	$139.91	13.274%	$158.4817	$158.48	$158.50	$158.50
Purchase #5	$230.34	6.103%	$244.3977	$244.40	$244.40	$244.40
Purchase #6	$92.46	3.575%	$95.7654	$95.77	$95.75	$95.80
Purchase #7	$34.71	11.444%	$38.6822	$38.68	$38.70	$38.70
7 purchase totals =	$601.85		$650.4870	$650.49	$650.50	$650.60