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	$55.93	6.606%	$59.6247	$59.62	$59.60	$59.60
Purchase #2	$165.53	4.504%	$172.9855	$172.99	$173.00	$173.00
Purchase #3	$200.25	8.767%	$217.8059	$217.81	$217.80	$217.80
Purchase #4	$27.70	10.331%	$30.5617	$30.56	$30.55	$30.60
Purchase #5	$133.65	7.404%	$143.5454	$143.55	$143.55	$143.50
Purchase #6	$64.79	13.410%	$73.4783	$73.48	$73.50	$73.50
Purchase #7	$50.60	11.622%	$56.4807	$56.48	$56.50	$56.50
7 purchase totals =	$698.45		$754.4822	$754.49	$754.50	$754.50