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	$38.79	9.538%	$42.4898	$42.49	$42.50	$42.50
Purchase #2	$130.25	5.845%	$137.8631	$137.86	$137.85	$137.90
Purchase #3	$102.63	8.797%	$111.6584	$111.66	$111.65	$111.70
Purchase #4	$125.77	4.657%	$131.6271	$131.63	$131.65	$131.60
Purchase #5	$67.58	5.291%	$71.1557	$71.16	$71.15	$71.20
Purchase #6	$40.41	13.623%	$45.9151	$45.92	$45.90	$45.90
Purchase #7	$63.42	11.633%	$70.7976	$70.80	$70.80	$70.80
7 purchase totals =	$568.85		$611.5068	$611.52	$611.50	$611.60