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	$123.87	13.438%	$140.5157	$140.52	$140.50	$140.50
Purchase #2	$117.93	7.161%	$126.375	$126.38	$126.40	$126.40
Purchase #3	$152.97	10.762%	$169.4326	$169.43	$169.45	$169.40
Purchase #4	$82.71	11.605%	$92.3085	$92.31	$92.30	$92.30
Purchase #5	$141.89	13.407%	$160.9132	$160.91	$160.90	$160.90
Purchase #6	$163.63	5.169%	$172.088	$172.09	$172.10	$172.10
Purchase #7	$63.56	3.656%	$65.8838	$65.88	$65.90	$65.90
7 purchase totals =	$846.56		$927.5168	$927.52	$927.55	$927.50