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	$190.92	13.709%	$217.0932	$217.09	$217.10	$217.10
Purchase #2	$35.61	5.764%	$37.6626	$37.66	$37.65	$37.70
Purchase #3	$57.45	10.656%	$63.5719	$63.57	$63.55	$63.60
Purchase #4	$38.71	5.482%	$40.8321	$40.83	$40.85	$40.80
Purchase #5	$162.77	13.845%	$185.3055	$185.31	$185.30	$185.30
Purchase #6	$155.93	8.511%	$169.2012	$169.20	$169.20	$169.20
Purchase #7	$81.49	10.635%	$90.1565	$90.16	$90.15	$90.20
7 purchase totals =	$722.88		$803.8230	$803.82	$803.80	$803.90