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	$210.81	3.381%	$217.9375	$217.94	$217.95	$217.90
Purchase #2	$138.51	6.766%	$147.8816	$147.88	$147.90	$147.90
Purchase #3	$192.51	12.798%	$217.1474	$217.15	$217.15	$217.10
Purchase #4	$170.59	11.525%	$190.2505	$190.25	$190.25	$190.30
Purchase #5	$249.87	4.398%	$260.8593	$260.86	$260.85	$260.90
Purchase #6	$242.72	13.496%	$275.4775	$275.48	$275.50	$275.50
Purchase #7	$6.55	5.797%	$6.9297	$6.93	$6.95	$6.90
7 purchase totals =	$1,211.56		$1,316.4835	$1,316.49	$1,316.55	$1,316.50