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	$152.42	11.770%	$170.3598	$170.36	$170.35	$170.40
Purchase #2	$144.93	9.175%	$158.2273	$158.23	$158.25	$158.20
Purchase #3	$100.37	8.610%	$109.0119	$109.01	$109.00	$109.00
Purchase #4	$95.42	4.323%	$99.545	$99.55	$99.55	$99.50
Purchase #5	$7.34	9.762%	$8.0565	$8.06	$8.05	$8.10
Purchase #6	$44.87	10.823%	$49.7263	$49.73	$49.75	$49.70
Purchase #7	$114.47	8.173%	$123.8256	$123.83	$123.85	$123.80
7 purchase totals =	$659.82		$718.7524	$718.77	$718.80	$718.70