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	$86.77	4.579%	$90.7432	$90.74	$90.75	$90.70
Purchase #2	$112.63	5.777%	$119.1366	$119.14	$119.15	$119.10
Purchase #3	$225.37	7.312%	$241.8491	$241.85	$241.85	$241.80
Purchase #4	$158.94	3.376%	$164.3058	$164.31	$164.30	$164.30
Purchase #5	$43.26	12.768%	$48.7834	$48.78	$48.80	$48.80
Purchase #6	$225.85	7.372%	$242.4997	$242.50	$242.50	$242.50
Purchase #7	$11.92	12.403%	$13.3984	$13.40	$13.40	$13.40
7 purchase totals =	$864.74		$920.7162	$920.72	$920.75	$920.60