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	$235.64	6.466%	$250.8765	$250.88	$250.90	$250.90
Purchase #2	$172.44	8.724%	$187.4837	$187.48	$187.50	$187.50
Purchase #3	$214.47	13.686%	$243.8224	$243.82	$243.80	$243.80
Purchase #4	$159.45	11.644%	$178.0164	$178.02	$178.00	$178.00
Purchase #5	$8.58	3.766%	$8.9031	$8.90	$8.90	$8.90
Purchase #6	$136.60	10.247%	$150.5974	$150.60	$150.60	$150.60
Purchase #7	$138.86	5.741%	$146.832	$146.83	$146.85	$146.80
7 purchase totals =	$1,066.04		$1,166.5315	$1,166.53	$1,166.55	$1,166.50