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	$11.57	7.672%	$12.4577	$12.46	$12.45	$12.50
Purchase #2	$84.51	5.570%	$89.2172	$89.22	$89.20	$89.20
Purchase #3	$171.56	13.359%	$194.4787	$194.48	$194.50	$194.50
Purchase #4	$248.47	4.537%	$259.7431	$259.74	$259.75	$259.70
Purchase #5	$41.60	11.647%	$46.4452	$46.45	$46.45	$46.40
Purchase #6	$180.60	6.644%	$192.5991	$192.60	$192.60	$192.60
Purchase #7	$155.70	5.845%	$164.8007	$164.80	$164.80	$164.80
7 purchase totals =	$894.01		$959.7417	$959.75	$959.75	$959.70