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	$21.79	9.861%	$23.9387	$23.94	$23.95	$23.90
Purchase #2	$191.35	7.440%	$205.5864	$205.59	$205.60	$205.60
Purchase #3	$36.96	8.314%	$40.0329	$40.03	$40.05	$40.00
Purchase #4	$165.78	4.221%	$172.7776	$172.78	$172.80	$172.80
Purchase #5	$236.55	6.481%	$251.8808	$251.88	$251.90	$251.90
Purchase #6	$166.38	3.720%	$172.5693	$172.57	$172.55	$172.60
Purchase #7	$29.85	7.757%	$32.1655	$32.17	$32.15	$32.20
7 purchase totals =	$848.66		$898.9512	$898.96	$899.00	$899.00