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	$35.61	13.799%	$40.5238	$40.52	$40.50	$40.50
Purchase #2	$136.68	11.859%	$152.8889	$152.89	$152.90	$152.90
Purchase #3	$17.81	10.545%	$19.6881	$19.69	$19.70	$19.70
Purchase #4	$16.56	4.326%	$17.2764	$17.28	$17.30	$17.30
Purchase #5	$204.60	9.208%	$223.4396	$223.44	$223.45	$223.40
Purchase #6	$111.70	6.612%	$119.0856	$119.09	$119.10	$119.10
Purchase #7	$72.93	6.680%	$77.8017	$77.80	$77.80	$77.80
7 purchase totals =	$595.89		$650.7041	$650.71	$650.75	$650.70