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	$98.54	13.172%	$111.5197	$111.52	$111.50	$111.50
Purchase #2	$150.83	6.553%	$160.7139	$160.71	$160.70	$160.70
Purchase #3	$119.86	9.420%	$131.1508	$131.15	$131.15	$131.20
Purchase #4	$40.87	6.247%	$43.4231	$43.42	$43.40	$43.40
Purchase #5	$140.63	9.714%	$154.2908	$154.29	$154.30	$154.30
Purchase #6	$172.26	5.317%	$181.4191	$181.42	$181.40	$181.40
Purchase #7	$119.69	11.622%	$133.6004	$133.60	$133.60	$133.60
7 purchase totals =	$842.68		$916.1178	$916.11	$916.05	$916.10