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	$49.94	13.364%	$56.614	$56.61	$56.60	$56.60
Purchase #2	$49.52	5.844%	$52.4139	$52.41	$52.40	$52.40
Purchase #3	$108.54	11.359%	$120.8691	$120.87	$120.85	$120.90
Purchase #4	$233.83	10.104%	$257.4562	$257.46	$257.45	$257.50
Purchase #5	$48.96	11.616%	$54.6472	$54.65	$54.65	$54.60
Purchase #6	$237.65	12.672%	$267.765	$267.77	$267.75	$267.80
Purchase #7	$111.86	3.807%	$116.1185	$116.12	$116.10	$116.10
7 purchase totals =	$840.30		$925.8839	$925.89	$925.80	$925.90