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	$47.27	8.820%	$51.4392	$51.44	$51.45	$51.40
Purchase #2	$41.74	11.769%	$46.6524	$46.65	$46.65	$46.70
Purchase #3	$78.50	13.645%	$89.2113	$89.21	$89.20	$89.20
Purchase #4	$44.55	4.491%	$46.5507	$46.55	$46.55	$46.60
Purchase #5	$57.79	8.390%	$62.6386	$62.64	$62.65	$62.60
Purchase #6	$46.38	4.631%	$48.5279	$48.53	$48.55	$48.50
Purchase #7	$154.39	11.722%	$172.4876	$172.49	$172.50	$172.50
7 purchase totals =	$470.62		$517.5077	$517.51	$517.55	$517.50