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	$85.48	12.113%	$95.8342	$95.83	$95.85	$95.80
Purchase #2	$121.80	7.870%	$131.3857	$131.39	$131.40	$131.40
Purchase #3	$208.64	10.448%	$230.4387	$230.44	$230.45	$230.40
Purchase #4	$111.59	5.787%	$118.0477	$118.05	$118.05	$118.00
Purchase #5	$34.49	13.530%	$39.1565	$39.16	$39.15	$39.20
Purchase #6	$112.75	6.295%	$119.8476	$119.85	$119.85	$119.80
Purchase #7	$13.86	7.230%	$14.8621	$14.86	$14.85	$14.90
7 purchase totals =	$688.61		$749.5725	$749.58	$749.60	$749.50