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	$85.35	7.309%	$91.5882	$91.59	$91.60	$91.60
Purchase #2	$57.93	8.103%	$62.6241	$62.62	$62.60	$62.60
Purchase #3	$239.65	4.146%	$249.5859	$249.59	$249.60	$249.60
Purchase #4	$32.51	12.391%	$36.5383	$36.54	$36.55	$36.50
Purchase #5	$112.95	13.188%	$127.8458	$127.85	$127.85	$127.80
Purchase #6	$209.39	7.660%	$225.4293	$225.43	$225.45	$225.40
Purchase #7	$10.62	3.389%	$10.9799	$10.98	$11.00	$11.00
7 purchase totals =	$748.40		$804.5915	$804.60	$804.65	$804.50