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	$227.82	9.697%	$249.9117	$249.91	$249.90	$249.90
Purchase #2	$35.63	12.823%	$40.1988	$40.20	$40.20	$40.20
Purchase #3	$59.28	13.671%	$67.3842	$67.38	$67.40	$67.40
Purchase #4	$249.83	6.845%	$266.9309	$266.93	$266.95	$266.90
Purchase #5	$231.96	7.314%	$248.9256	$248.93	$248.95	$248.90
Purchase #6	$172.83	6.138%	$183.4383	$183.44	$183.45	$183.40
Purchase #7	$112.64	9.395%	$123.2225	$123.22	$123.20	$123.20
7 purchase totals =	$1,089.99		$1,180.0120	$1,180.01	$1,180.05	$1,179.90