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	$134.80	13.172%	$152.5559	$152.56	$152.55	$152.60
Purchase #2	$111.95	10.180%	$123.3465	$123.35	$123.35	$123.30
Purchase #3	$34.50	3.149%	$35.5864	$35.59	$35.60	$35.60
Purchase #4	$68.35	12.278%	$76.742	$76.74	$76.75	$76.70
Purchase #5	$94.47	8.706%	$102.6946	$102.69	$102.70	$102.70
Purchase #6	$166.86	7.159%	$178.8055	$178.81	$178.80	$178.80
Purchase #7	$62.71	4.105%	$65.2842	$65.28	$65.30	$65.30
7 purchase totals =	$673.64		$735.0151	$735.02	$735.05	$735.00