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	$80.31	13.572%	$91.2097	$91.21	$91.20	$91.20
Purchase #2	$114.27	5.402%	$120.4429	$120.44	$120.45	$120.40
Purchase #3	$230.52	8.214%	$249.4549	$249.45	$249.45	$249.50
Purchase #4	$9.27	4.809%	$9.7158	$9.72	$9.70	$9.70
Purchase #5	$237.57	8.849%	$258.5926	$258.59	$258.60	$258.60
Purchase #6	$95.85	10.120%	$105.55	$105.55	$105.55	$105.60
Purchase #7	$99.85	5.723%	$105.5644	$105.56	$105.55	$105.60
7 purchase totals =	$867.64		$940.5303	$940.52	$940.50	$940.60