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	$167.60	7.442%	$180.0728	$180.07	$180.05	$180.10
Purchase #2	$106.67	12.426%	$119.9248	$119.92	$119.90	$119.90
Purchase #3	$87.49	3.758%	$90.7779	$90.78	$90.80	$90.80
Purchase #4	$94.62	11.136%	$105.1569	$105.16	$105.15	$105.20
Purchase #5	$57.26	3.330%	$59.1668	$59.17	$59.15	$59.20
Purchase #6	$164.62	8.675%	$178.9008	$178.90	$178.90	$178.90
Purchase #7	$200.51	8.487%	$217.5273	$217.53	$217.55	$217.50
7 purchase totals =	$878.77		$951.5273	$951.53	$951.50	$951.60