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	$236.78	7.354%	$254.1928	$254.19	$254.20	$254.20
Purchase #2	$142.43	4.200%	$148.4121	$148.41	$148.40	$148.40
Purchase #3	$119.82	3.218%	$123.6758	$123.68	$123.70	$123.70
Purchase #4	$36.25	10.619%	$40.0994	$40.10	$40.10	$40.10
Purchase #5	$79.68	13.858%	$90.7221	$90.72	$90.70	$90.70
Purchase #6	$157.82	13.390%	$178.9521	$178.95	$178.95	$179.00
Purchase #7	$217.78	7.235%	$233.5364	$233.54	$233.55	$233.50
7 purchase totals =	$990.56		$1,069.5907	$1,069.59	$1,069.60	$1,069.60