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	$106.30	13.287%	$120.4241	$120.42	$120.40	$120.40
Purchase #2	$66.40	6.108%	$70.4557	$70.46	$70.45	$70.50
Purchase #3	$91.87	13.828%	$104.5738	$104.57	$104.55	$104.60
Purchase #4	$200.81	10.286%	$221.4653	$221.47	$221.45	$221.50
Purchase #5	$36.73	5.131%	$38.6146	$38.61	$38.60	$38.60
Purchase #6	$139.52	13.360%	$158.1599	$158.16	$158.15	$158.20
Purchase #7	$94.65	12.461%	$106.4443	$106.44	$106.45	$106.40
7 purchase totals =	$736.28		$820.1377	$820.13	$820.05	$820.20