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	$239.65	6.247%	$254.6209	$254.62	$254.60	$254.60
Purchase #2	$95.65	5.294%	$100.7137	$100.71	$100.70	$100.70
Purchase #3	$64.48	3.139%	$66.504	$66.50	$66.50	$66.50
Purchase #4	$101.52	4.208%	$105.792	$105.79	$105.80	$105.80
Purchase #5	$138.53	6.562%	$147.6203	$147.62	$147.60	$147.60
Purchase #6	$45.96	9.422%	$50.2904	$50.29	$50.30	$50.30
Purchase #7	$27.88	11.174%	$30.9953	$31.00	$31.00	$31.00
7 purchase totals =	$713.67		$756.5366	$756.53	$756.50	$756.50