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	$39.37	8.239%	$42.6137	$42.61	$42.60	$42.60
Purchase #2	$82.44	13.140%	$93.2726	$93.27	$93.25	$93.30
Purchase #3	$144.52	9.122%	$157.7031	$157.70	$157.70	$157.70
Purchase #4	$137.83	12.403%	$154.9251	$154.93	$154.95	$154.90
Purchase #5	$141.90	12.650%	$159.8504	$159.85	$159.85	$159.90
Purchase #6	$241.69	5.866%	$255.8675	$255.87	$255.85	$255.90
Purchase #7	$96.28	4.281%	$100.4017	$100.40	$100.40	$100.40
7 purchase totals =	$884.03		$964.6341	$964.63	$964.60	$964.70