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	$205.76	5.689%	$217.4657	$217.47	$217.45	$217.50
Purchase #2	$52.92	9.147%	$57.7606	$57.76	$57.75	$57.80
Purchase #3	$141.58	8.440%	$153.5294	$153.53	$153.55	$153.50
Purchase #4	$41.25	3.809%	$42.8212	$42.82	$42.80	$42.80
Purchase #5	$99.49	11.639%	$111.0696	$111.07	$111.05	$111.10
Purchase #6	$135.85	12.758%	$153.1817	$153.18	$153.20	$153.20
Purchase #7	$65.95	9.364%	$72.1256	$72.13	$72.15	$72.10
7 purchase totals =	$742.80		$807.9538	$807.96	$807.95	$808.00