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	$131.54	4.195%	$137.0581	$137.06	$137.05	$137.10
Purchase #2	$20.81	3.189%	$21.4736	$21.47	$21.45	$21.50
Purchase #3	$16.76	4.809%	$17.566	$17.57	$17.55	$17.60
Purchase #4	$162.45	6.214%	$172.5446	$172.54	$172.55	$172.50
Purchase #5	$34.74	10.661%	$38.4436	$38.44	$38.45	$38.40
Purchase #6	$217.97	10.128%	$240.046	$240.05	$240.05	$240.00
Purchase #7	$248.87	12.706%	$280.4914	$280.49	$280.50	$280.50
7 purchase totals =	$833.14		$907.6233	$907.62	$907.60	$907.60