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	$246.94	8.103%	$266.9495	$266.95	$266.95	$266.90
Purchase #2	$83.86	11.620%	$93.6045	$93.60	$93.60	$93.60
Purchase #3	$89.65	12.106%	$100.503	$100.50	$100.50	$100.50
Purchase #4	$89.49	8.855%	$97.4143	$97.41	$97.40	$97.40
Purchase #5	$138.78	4.221%	$144.6379	$144.64	$144.65	$144.60
Purchase #6	$137.80	9.349%	$150.6829	$150.68	$150.70	$150.70
Purchase #7	$57.90	8.113%	$62.5974	$62.60	$62.60	$62.60
7 purchase totals =	$844.42		$916.3895	$916.38	$916.40	$916.30