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	$231.52	13.842%	$263.567	$263.57	$263.55	$263.60
Purchase #2	$181.27	8.349%	$196.4042	$196.40	$196.40	$196.40
Purchase #3	$177.35	4.576%	$185.4655	$185.47	$185.45	$185.50
Purchase #4	$16.69	5.816%	$17.6607	$17.66	$17.65	$17.70
Purchase #5	$120.65	11.465%	$134.4825	$134.48	$134.50	$134.50
Purchase #6	$151.60	4.695%	$158.7176	$158.72	$158.70	$158.70
Purchase #7	$21.83	7.301%	$23.4238	$23.42	$23.40	$23.40
7 purchase totals =	$900.91		$979.7213	$979.72	$979.65	$979.80