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	$18.47	6.188%	$19.6129	$19.61	$19.60	$19.60
Purchase #2	$42.45	3.469%	$43.9226	$43.92	$43.90	$43.90
Purchase #3	$92.85	10.509%	$102.6076	$102.61	$102.60	$102.60
Purchase #4	$56.87	8.657%	$61.7932	$61.79	$61.80	$61.80
Purchase #5	$215.29	11.782%	$240.6555	$240.66	$240.65	$240.70
Purchase #6	$128.42	11.104%	$142.6798	$142.68	$142.70	$142.70
Purchase #7	$35.48	13.445%	$40.2503	$40.25	$40.25	$40.30
7 purchase totals =	$589.83		$651.5219	$651.52	$651.50	$651.60