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	$98.84	12.340%	$111.0369	$111.04	$111.05	$111.00
Purchase #2	$139.43	12.764%	$157.2268	$157.23	$157.25	$157.20
Purchase #3	$77.53	8.238%	$83.9169	$83.92	$83.90	$83.90
Purchase #4	$52.31	10.605%	$57.8575	$57.86	$57.85	$57.90
Purchase #5	$134.67	13.751%	$153.1885	$153.19	$153.20	$153.20
Purchase #6	$101.49	13.202%	$114.8887	$114.89	$114.90	$114.90
Purchase #7	$145.76	10.751%	$161.4307	$161.43	$161.45	$161.40
7 purchase totals =	$750.03		$839.5460	$839.56	$839.60	$839.50