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	$159.53	8.556%	$173.1794	$173.18	$173.20	$173.20
Purchase #2	$140.48	3.871%	$145.918	$145.92	$145.90	$145.90
Purchase #3	$216.44	11.483%	$241.2938	$241.29	$241.30	$241.30
Purchase #4	$89.30	12.540%	$100.4982	$100.50	$100.50	$100.50
Purchase #5	$146.72	9.763%	$161.0443	$161.04	$161.05	$161.00
Purchase #6	$111.64	6.506%	$118.9033	$118.90	$118.90	$118.90
Purchase #7	$125.86	12.382%	$141.444	$141.44	$141.45	$141.40
7 purchase totals =	$989.97		$1,082.2810	$1,082.27	$1,082.30	$1,082.20