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	$88.43	13.559%	$100.4202	$100.42	$100.40	$100.40
Purchase #2	$214.98	12.303%	$241.429	$241.43	$241.45	$241.40
Purchase #3	$212.70	10.532%	$235.1016	$235.10	$235.10	$235.10
Purchase #4	$206.66	11.455%	$230.3329	$230.33	$230.35	$230.30
Purchase #5	$127.46	9.124%	$139.0895	$139.09	$139.10	$139.10
Purchase #6	$199.55	6.482%	$212.4848	$212.48	$212.50	$212.50
Purchase #7	$118.80	10.792%	$131.6209	$131.62	$131.60	$131.60
7 purchase totals =	$1,168.58		$1,290.4789	$1,290.47	$1,290.50	$1,290.40