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	$10.67	11.459%	$11.8927	$11.89	$11.90	$11.90
Purchase #2	$245.69	13.333%	$278.4478	$278.45	$278.45	$278.40
Purchase #3	$159.78	13.521%	$181.3839	$181.38	$181.40	$181.40
Purchase #4	$124.93	5.720%	$132.076	$132.08	$132.10	$132.10
Purchase #5	$159.84	5.391%	$168.457	$168.46	$168.45	$168.50
Purchase #6	$236.52	12.379%	$265.7988	$265.80	$265.80	$265.80
Purchase #7	$80.61	6.181%	$85.5925	$85.59	$85.60	$85.60
7 purchase totals =	$1,018.04		$1,123.6487	$1,123.65	$1,123.70	$1,123.70