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	$215.49	6.128%	$228.6952	$228.70	$228.70	$228.70
Purchase #2	$99.55	8.464%	$107.9759	$107.98	$108.00	$108.00
Purchase #3	$185.38	12.285%	$208.1539	$208.15	$208.15	$208.20
Purchase #4	$244.42	12.821%	$275.7571	$275.76	$275.75	$275.80
Purchase #5	$144.83	13.212%	$163.9649	$163.96	$163.95	$164.00
Purchase #6	$72.43	8.283%	$78.4294	$78.43	$78.45	$78.40
Purchase #7	$38.75	10.531%	$42.8308	$42.83	$42.85	$42.80
7 purchase totals =	$1,000.85		$1,105.8072	$1,105.81	$1,105.85	$1,105.90