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	$126.71	13.752%	$144.1352	$144.14	$144.15	$144.10
Purchase #2	$206.94	3.699%	$214.5947	$214.59	$214.60	$214.60
Purchase #3	$137.30	11.722%	$153.3943	$153.39	$153.40	$153.40
Purchase #4	$79.83	11.724%	$89.1893	$89.19	$89.20	$89.20
Purchase #5	$33.26	12.485%	$37.4125	$37.41	$37.40	$37.40
Purchase #6	$222.46	11.490%	$248.0207	$248.02	$248.00	$248.00
Purchase #7	$17.81	5.770%	$18.8376	$18.84	$18.85	$18.80
7 purchase totals =	$824.31		$905.5843	$905.58	$905.60	$905.50