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	$234.29	3.438%	$242.3449	$242.34	$242.35	$242.30
Purchase #2	$172.47	10.442%	$190.4793	$190.48	$190.50	$190.50
Purchase #3	$244.25	5.208%	$256.9705	$256.97	$256.95	$257.00
Purchase #4	$16.83	11.512%	$18.7675	$18.77	$18.75	$18.80
Purchase #5	$77.32	5.547%	$81.6089	$81.61	$81.60	$81.60
Purchase #6	$40.28	4.491%	$42.089	$42.09	$42.10	$42.10
Purchase #7	$128.40	6.739%	$137.0529	$137.05	$137.05	$137.10
7 purchase totals =	$913.84		$969.3130	$969.31	$969.30	$969.40