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	$113.55	13.344%	$128.7021	$128.70	$128.70	$128.70
Purchase #2	$86.46	6.317%	$91.9217	$91.92	$91.90	$91.90
Purchase #3	$64.40	3.258%	$66.4982	$66.50	$66.50	$66.50
Purchase #4	$83.68	7.773%	$90.1844	$90.18	$90.20	$90.20
Purchase #5	$92.90	8.398%	$100.7017	$100.70	$100.70	$100.70
Purchase #6	$219.79	13.108%	$248.6001	$248.60	$248.60	$248.60
Purchase #7	$132.29	8.750%	$143.8654	$143.87	$143.85	$143.90
7 purchase totals =	$793.07		$870.4736	$870.47	$870.45	$870.50