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	$6.48	5.359%	$6.8273	$6.83	$6.85	$6.80
Purchase #2	$154.46	4.335%	$161.1558	$161.16	$161.15	$161.20
Purchase #3	$26.39	11.395%	$29.3971	$29.40	$29.40	$29.40
Purchase #4	$99.76	13.178%	$112.9064	$112.91	$112.90	$112.90
Purchase #5	$116.72	9.423%	$127.7185	$127.72	$127.70	$127.70
Purchase #6	$37.44	10.750%	$41.4648	$41.46	$41.45	$41.50
Purchase #7	$134.29	7.761%	$144.7122	$144.71	$144.70	$144.70
7 purchase totals =	$575.54		$624.1821	$624.19	$624.15	$624.20