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	$9.50	10.644%	$10.5112	$10.51	$10.50	$10.50
Purchase #2	$55.71	8.781%	$60.6019	$60.60	$60.60	$60.60
Purchase #3	$177.54	11.670%	$198.2589	$198.26	$198.25	$198.30
Purchase #4	$204.54	13.190%	$231.5188	$231.52	$231.50	$231.50
Purchase #5	$144.82	6.405%	$154.0957	$154.10	$154.10	$154.10
Purchase #6	$116.56	13.512%	$132.3096	$132.31	$132.30	$132.30
Purchase #7	$238.87	8.622%	$259.4654	$259.47	$259.45	$259.50
7 purchase totals =	$947.54		$1,046.7615	$1,046.77	$1,046.70	$1,046.80