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	$31.87	8.714%	$34.6472	$34.65	$34.65	$34.60
Purchase #2	$53.55	11.239%	$59.5685	$59.57	$59.55	$59.60
Purchase #3	$114.27	7.703%	$123.0722	$123.07	$123.05	$123.10
Purchase #4	$113.93	7.755%	$122.7653	$122.77	$122.75	$122.80
Purchase #5	$113.46	9.185%	$123.8813	$123.88	$123.90	$123.90
Purchase #6	$40.97	12.720%	$46.1814	$46.18	$46.20	$46.20
Purchase #7	$48.77	13.622%	$55.4134	$55.41	$55.40	$55.40
7 purchase totals =	$516.82		$565.5293	$565.53	$565.50	$565.60