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	$159.92	4.318%	$166.8253	$166.83	$166.85	$166.80
Purchase #2	$137.82	7.839%	$148.6237	$148.62	$148.60	$148.60
Purchase #3	$227.27	12.547%	$255.7856	$255.79	$255.80	$255.80
Purchase #4	$66.56	10.106%	$73.2866	$73.29	$73.30	$73.30
Purchase #5	$134.26	3.181%	$138.5308	$138.53	$138.55	$138.50
Purchase #6	$103.85	12.286%	$116.609	$116.61	$116.60	$116.60
Purchase #7	$14.77	7.745%	$15.9139	$15.91	$15.90	$15.90
7 purchase totals =	$844.45		$915.5749	$915.58	$915.60	$915.50