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	$76.83	5.618%	$81.1463	$81.15	$81.15	$81.10
Purchase #2	$103.41	12.265%	$116.0932	$116.09	$116.10	$116.10
Purchase #3	$128.39	12.444%	$144.3669	$144.37	$144.35	$144.40
Purchase #4	$53.28	10.739%	$59.0017	$59.00	$59.00	$59.00
Purchase #5	$176.38	3.445%	$182.4563	$182.46	$182.45	$182.50
Purchase #6	$172.58	3.498%	$178.6168	$178.62	$178.60	$178.60
Purchase #7	$191.74	13.383%	$217.4006	$217.40	$217.40	$217.40
7 purchase totals =	$902.61		$979.0818	$979.09	$979.05	$979.10