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	$139.43	4.369%	$145.5217	$145.52	$145.50	$145.50
Purchase #2	$83.80	8.316%	$90.7688	$90.77	$90.75	$90.80
Purchase #3	$146.89	12.677%	$165.5112	$165.51	$165.50	$165.50
Purchase #4	$19.36	11.217%	$21.5316	$21.53	$21.55	$21.50
Purchase #5	$44.60	7.288%	$47.8504	$47.85	$47.85	$47.90
Purchase #6	$72.58	7.456%	$77.9916	$77.99	$78.00	$78.00
Purchase #7	$116.32	5.641%	$122.8816	$122.88	$122.90	$122.90
7 purchase totals =	$622.98		$672.0569	$672.05	$672.05	$672.10