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	$19.71	9.195%	$21.5223	$21.52	$21.50	$21.50
Purchase #2	$47.27	10.147%	$52.0665	$52.07	$52.05	$52.10
Purchase #3	$50.30	4.248%	$52.4367	$52.44	$52.45	$52.40
Purchase #4	$7.92	5.818%	$8.3808	$8.38	$8.40	$8.40
Purchase #5	$41.63	9.188%	$45.455	$45.46	$45.45	$45.50
Purchase #6	$63.64	11.177%	$70.753	$70.75	$70.75	$70.80
Purchase #7	$198.63	5.175%	$208.9091	$208.91	$208.90	$208.90
7 purchase totals =	$429.10		$459.5234	$459.53	$459.50	$459.60