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	$38.66	10.260%	$42.6265	$42.63	$42.65	$42.60
Purchase #2	$33.62	7.828%	$36.2518	$36.25	$36.25	$36.30
Purchase #3	$30.87	12.751%	$34.8062	$34.81	$34.80	$34.80
Purchase #4	$135.77	6.485%	$144.5747	$144.57	$144.55	$144.60
Purchase #5	$42.58	13.462%	$48.3121	$48.31	$48.30	$48.30
Purchase #6	$223.83	7.253%	$240.0644	$240.06	$240.05	$240.10
Purchase #7	$225.68	13.329%	$255.7609	$255.76	$255.75	$255.80
7 purchase totals =	$731.01		$802.3966	$802.39	$802.35	$802.50