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	$67.44	7.450%	$72.4643	$72.46	$72.45	$72.50
Purchase #2	$112.73	9.691%	$123.6547	$123.65	$123.65	$123.70
Purchase #3	$44.68	8.464%	$48.4617	$48.46	$48.45	$48.50
Purchase #4	$87.89	10.514%	$97.1308	$97.13	$97.15	$97.10
Purchase #5	$240.25	8.565%	$260.8274	$260.83	$260.85	$260.80
Purchase #6	$229.85	8.151%	$248.5851	$248.59	$248.60	$248.60
Purchase #7	$131.38	6.389%	$139.7739	$139.77	$139.75	$139.80
7 purchase totals =	$914.22		$990.8979	$990.89	$990.90	$991.00