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	$12.74	3.281%	$13.158	$13.16	$13.15	$13.20
Purchase #2	$247.89	4.430%	$258.8715	$258.87	$258.85	$258.90
Purchase #3	$88.45	11.633%	$98.7394	$98.74	$98.75	$98.70
Purchase #4	$143.83	10.608%	$159.0875	$159.09	$159.10	$159.10
Purchase #5	$109.73	6.210%	$116.5442	$116.54	$116.55	$116.50
Purchase #6	$212.94	8.769%	$231.6127	$231.61	$231.60	$231.60
Purchase #7	$223.54	11.733%	$249.7679	$249.77	$249.75	$249.80
7 purchase totals =	$1,039.12		$1,127.7812	$1,127.78	$1,127.75	$1,127.80