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	$55.31	6.690%	$59.0102	$59.01	$59.00	$59.00
Purchase #2	$38.93	6.280%	$41.3748	$41.37	$41.35	$41.40
Purchase #3	$204.60	13.215%	$231.6379	$231.64	$231.65	$231.60
Purchase #4	$132.82	3.617%	$137.6241	$137.62	$137.60	$137.60
Purchase #5	$16.68	10.715%	$18.4673	$18.47	$18.45	$18.50
Purchase #6	$13.85	12.415%	$15.5695	$15.57	$15.55	$15.60
Purchase #7	$115.64	11.366%	$128.7836	$128.78	$128.80	$128.80
7 purchase totals =	$577.83		$632.4674	$632.46	$632.40	$632.50