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	$6.58	12.384%	$7.3949	$7.39	$7.40	$7.40
Purchase #2	$190.26	12.855%	$214.7179	$214.72	$214.70	$214.70
Purchase #3	$137.87	10.854%	$152.8344	$152.83	$152.85	$152.80
Purchase #4	$162.60	6.546%	$173.2438	$173.24	$173.25	$173.20
Purchase #5	$91.83	8.358%	$99.5052	$99.51	$99.50	$99.50
Purchase #6	$61.65	8.665%	$66.992	$66.99	$67.00	$67.00
Purchase #7	$44.59	6.149%	$47.3318	$47.33	$47.35	$47.30
7 purchase totals =	$695.38		$762.0200	$762.01	$762.05	$761.90