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	$24.87	10.389%	$27.4537	$27.45	$27.45	$27.50
Purchase #2	$17.54	5.677%	$18.5357	$18.54	$18.55	$18.50
Purchase #3	$29.64	12.331%	$33.2949	$33.29	$33.30	$33.30
Purchase #4	$52.97	6.385%	$56.3521	$56.35	$56.35	$56.40
Purchase #5	$45.25	6.405%	$48.1483	$48.15	$48.15	$48.10
Purchase #6	$55.72	12.284%	$62.5646	$62.56	$62.55	$62.60
Purchase #7	$10.94	5.704%	$11.564	$11.56	$11.55	$11.60
7 purchase totals =	$236.93		$257.9133	$257.90	$257.90	$258.00