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	$24.63	9.682%	$27.0147	$27.01	$27.00	$27.00
Purchase #2	$66.86	13.676%	$76.0038	$76.00	$76.00	$76.00
Purchase #3	$77.56	10.240%	$85.5021	$85.50	$85.50	$85.50
Purchase #4	$158.96	10.556%	$175.7398	$175.74	$175.75	$175.70
Purchase #5	$155.95	11.313%	$173.5926	$173.59	$173.60	$173.60
Purchase #6	$138.90	9.341%	$151.8746	$151.87	$151.85	$151.90
Purchase #7	$108.25	3.138%	$111.6469	$111.65	$111.65	$111.60
7 purchase totals =	$731.11		$801.3745	$801.36	$801.35	$801.30