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	$76.50	6.114%	$81.1772	$81.18	$81.20	$81.20
Purchase #2	$134.64	12.175%	$151.0324	$151.03	$151.05	$151.00
Purchase #3	$90.45	9.659%	$99.1866	$99.19	$99.20	$99.20
Purchase #4	$77.78	13.777%	$88.4958	$88.50	$88.50	$88.50
Purchase #5	$10.55	6.181%	$11.2021	$11.20	$11.20	$11.20
Purchase #6	$88.48	12.534%	$99.5701	$99.57	$99.55	$99.60
Purchase #7	$23.49	9.776%	$25.7864	$25.79	$25.80	$25.80
7 purchase totals =	$501.89		$556.4506	$556.46	$556.50	$556.50