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	$169.67	8.226%	$183.6271	$183.63	$183.65	$183.60
Purchase #2	$114.50	10.267%	$126.2557	$126.26	$126.25	$126.30
Purchase #3	$153.49	8.131%	$165.9703	$165.97	$165.95	$166.00
Purchase #4	$97.29	3.562%	$100.7555	$100.76	$100.75	$100.80
Purchase #5	$79.78	9.533%	$87.3854	$87.39	$87.40	$87.40
Purchase #6	$43.59	5.108%	$45.8166	$45.82	$45.80	$45.80
Purchase #7	$100.92	4.841%	$105.8055	$105.81	$105.80	$105.80
7 purchase totals =	$759.24		$815.6161	$815.64	$815.60	$815.70