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	$131.44	8.185%	$142.1984	$142.20	$142.20	$142.20
Purchase #2	$148.94	10.491%	$164.5653	$164.57	$164.55	$164.60
Purchase #3	$86.64	9.196%	$94.6074	$94.61	$94.60	$94.60
Purchase #4	$16.90	12.825%	$19.0674	$19.07	$19.05	$19.10
Purchase #5	$198.31	12.221%	$222.5455	$222.55	$222.55	$222.50
Purchase #6	$236.39	9.794%	$259.542	$259.54	$259.55	$259.50
Purchase #7	$121.81	12.751%	$137.342	$137.34	$137.35	$137.30
7 purchase totals =	$940.43		$1,039.8680	$1,039.88	$1,039.85	$1,039.80