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	$27.78	13.872%	$31.6336	$31.63	$31.65	$31.60
Purchase #2	$90.58	9.826%	$99.4804	$99.48	$99.50	$99.50
Purchase #3	$27.61	8.769%	$30.0311	$30.03	$30.05	$30.00
Purchase #4	$220.45	12.785%	$248.6345	$248.63	$248.65	$248.60
Purchase #5	$127.70	12.404%	$143.5399	$143.54	$143.55	$143.50
Purchase #6	$20.99	12.509%	$23.6156	$23.62	$23.60	$23.60
Purchase #7	$175.92	11.433%	$196.0329	$196.03	$196.05	$196.00
7 purchase totals =	$691.03		$772.9680	$772.96	$773.05	$772.80