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	$136.69	9.732%	$149.9927	$149.99	$150.00	$150.00
Purchase #2	$153.52	12.788%	$173.1521	$173.15	$173.15	$173.20
Purchase #3	$42.53	13.509%	$48.2754	$48.28	$48.30	$48.30
Purchase #4	$7.72	11.752%	$8.6273	$8.63	$8.65	$8.60
Purchase #5	$131.38	10.230%	$144.8202	$144.82	$144.80	$144.80
Purchase #6	$105.54	5.467%	$111.3099	$111.31	$111.30	$111.30
Purchase #7	$103.56	7.204%	$111.0205	$111.02	$111.00	$111.00
7 purchase totals =	$680.94		$747.1981	$747.20	$747.20	$747.20