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	$234.31	9.225%	$255.9251	$255.93	$255.95	$255.90
Purchase #2	$10.37	11.416%	$11.5538	$11.55	$11.55	$11.60
Purchase #3	$96.55	7.462%	$103.7546	$103.75	$103.75	$103.80
Purchase #4	$94.52	5.686%	$99.8944	$99.89	$99.90	$99.90
Purchase #5	$132.66	3.723%	$137.5989	$137.60	$137.60	$137.60
Purchase #6	$122.88	4.839%	$128.8262	$128.83	$128.85	$128.80
Purchase #7	$46.64	12.349%	$52.3996	$52.40	$52.40	$52.40
7 purchase totals =	$737.93		$789.9526	$789.95	$790.00	$790.00