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	$46.79	8.208%	$50.6305	$50.63	$50.65	$50.60
Purchase #2	$228.37	3.583%	$236.5525	$236.55	$236.55	$236.60
Purchase #3	$126.75	6.129%	$134.5185	$134.52	$134.50	$134.50
Purchase #4	$59.98	11.760%	$67.0336	$67.03	$67.05	$67.00
Purchase #5	$44.68	12.145%	$50.1064	$50.11	$50.10	$50.10
Purchase #6	$79.89	6.858%	$85.3689	$85.37	$85.35	$85.40
Purchase #7	$14.52	5.724%	$15.3511	$15.35	$15.35	$15.40
7 purchase totals =	$600.98		$639.5615	$639.56	$639.55	$639.60