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	$18.44	3.797%	$19.1402	$19.14	$19.15	$19.10
Purchase #2	$118.52	10.842%	$131.3699	$131.37	$131.35	$131.40
Purchase #3	$56.55	5.303%	$59.5488	$59.55	$59.55	$59.50
Purchase #4	$106.45	5.780%	$112.6028	$112.60	$112.60	$112.60
Purchase #5	$183.52	8.522%	$199.1596	$199.16	$199.15	$199.20
Purchase #6	$187.61	13.509%	$212.9542	$212.95	$212.95	$213.00
Purchase #7	$77.57	13.199%	$87.8085	$87.81	$87.80	$87.80
7 purchase totals =	$748.66		$822.5840	$822.58	$822.55	$822.60