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	$114.87	11.773%	$128.3936	$128.39	$128.40	$128.40
Purchase #2	$144.78	12.418%	$162.7588	$162.76	$162.75	$162.80
Purchase #3	$76.39	13.345%	$86.5842	$86.58	$86.60	$86.60
Purchase #4	$116.89	3.658%	$121.1658	$121.17	$121.15	$121.20
Purchase #5	$18.88	3.440%	$19.5295	$19.53	$19.55	$19.50
Purchase #6	$52.72	7.757%	$56.8095	$56.81	$56.80	$56.80
Purchase #7	$88.68	12.293%	$99.5814	$99.58	$99.60	$99.60
7 purchase totals =	$613.21		$674.8228	$674.82	$674.85	$674.90