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	$77.41	3.702%	$80.2757	$80.28	$80.30	$80.30
Purchase #2	$210.51	13.313%	$238.5352	$238.54	$238.55	$238.50
Purchase #3	$112.42	9.750%	$123.381	$123.38	$123.40	$123.40
Purchase #4	$38.54	5.237%	$40.5583	$40.56	$40.55	$40.60
Purchase #5	$137.58	4.493%	$143.7615	$143.76	$143.75	$143.80
Purchase #6	$104.99	6.279%	$111.5823	$111.58	$111.60	$111.60
Purchase #7	$194.97	6.768%	$208.1656	$208.17	$208.15	$208.20
7 purchase totals =	$876.42		$946.2596	$946.27	$946.30	$946.40