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	$223.87	4.298%	$233.4919	$233.49	$233.50	$233.50
Purchase #2	$11.63	12.526%	$13.0868	$13.09	$13.10	$13.10
Purchase #3	$192.36	11.372%	$214.2352	$214.24	$214.25	$214.20
Purchase #4	$82.99	7.864%	$89.5163	$89.52	$89.50	$89.50
Purchase #5	$126.74	8.427%	$137.4204	$137.42	$137.40	$137.40
Purchase #6	$207.31	8.230%	$224.3716	$224.37	$224.35	$224.40
Purchase #7	$25.59	11.359%	$28.4968	$28.50	$28.50	$28.50
7 purchase totals =	$870.49		$940.6190	$940.63	$940.60	$940.60