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	$230.90	10.192%	$254.4333	$254.43	$254.45	$254.40
Purchase #2	$160.73	3.189%	$165.8557	$165.86	$165.85	$165.90
Purchase #3	$90.89	10.181%	$100.1435	$100.14	$100.15	$100.10
Purchase #4	$155.32	11.567%	$173.2859	$173.29	$173.30	$173.30
Purchase #5	$60.72	3.658%	$62.9411	$62.94	$62.95	$62.90
Purchase #6	$56.81	11.716%	$63.4659	$63.47	$63.45	$63.50
Purchase #7	$41.31	13.719%	$46.9773	$46.98	$47.00	$47.00
7 purchase totals =	$796.68		$867.1027	$867.11	$867.15	$867.10