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	$12.83	6.834%	$13.7068	$13.71	$13.70	$13.70
Purchase #2	$238.55	6.733%	$254.6116	$254.61	$254.60	$254.60
Purchase #3	$75.90	12.815%	$85.6266	$85.63	$85.65	$85.60
Purchase #4	$102.90	6.229%	$109.3096	$109.31	$109.30	$109.30
Purchase #5	$137.50	7.779%	$148.1961	$148.20	$148.20	$148.20
Purchase #6	$112.83	12.482%	$126.9134	$126.91	$126.90	$126.90
Purchase #7	$74.62	12.232%	$83.7475	$83.75	$83.75	$83.70
7 purchase totals =	$755.13		$822.1116	$822.12	$822.10	$822.00