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	$135.64	6.727%	$144.7645	$144.76	$144.75	$144.80
Purchase #2	$41.82	8.438%	$45.3488	$45.35	$45.35	$45.30
Purchase #3	$234.47	5.252%	$246.7844	$246.78	$246.80	$246.80
Purchase #4	$29.42	6.630%	$31.3705	$31.37	$31.35	$31.40
Purchase #5	$100.81	7.609%	$108.4806	$108.48	$108.50	$108.50
Purchase #6	$111.95	10.103%	$123.2603	$123.26	$123.25	$123.30
Purchase #7	$14.72	7.477%	$15.8206	$15.82	$15.80	$15.80
7 purchase totals =	$668.83		$715.8297	$715.82	$715.80	$715.90