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	$49.52	13.594%	$56.2517	$56.25	$56.25	$56.30
Purchase #2	$125.92	4.255%	$131.2779	$131.28	$131.30	$131.30
Purchase #3	$67.29	11.283%	$74.8823	$74.88	$74.90	$74.90
Purchase #4	$106.47	9.815%	$116.92	$116.92	$116.90	$116.90
Purchase #5	$62.72	6.828%	$67.0025	$67.00	$67.00	$67.00
Purchase #6	$40.81	13.368%	$46.2655	$46.27	$46.25	$46.30
Purchase #7	$174.27	7.553%	$187.4326	$187.43	$187.45	$187.40
7 purchase totals =	$627.00		$680.0325	$680.03	$680.05	$680.10