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	$19.27	13.456%	$21.863	$21.86	$21.85	$21.90
Purchase #2	$21.35	5.856%	$22.6003	$22.60	$22.60	$22.60
Purchase #3	$53.28	7.619%	$57.3394	$57.34	$57.35	$57.30
Purchase #4	$240.89	8.121%	$260.4527	$260.45	$260.45	$260.50
Purchase #5	$124.64	10.410%	$137.615	$137.62	$137.60	$137.60
Purchase #6	$74.75	10.111%	$82.308	$82.31	$82.30	$82.30
Purchase #7	$228.27	3.509%	$236.28	$236.28	$236.30	$236.30
7 purchase totals =	$762.45		$818.4584	$818.46	$818.45	$818.50