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	$169.47	5.412%	$178.6417	$178.64	$178.65	$178.60
Purchase #2	$248.71	12.781%	$280.4976	$280.50	$280.50	$280.50
Purchase #3	$116.59	10.459%	$128.7841	$128.78	$128.80	$128.80
Purchase #4	$62.78	5.718%	$66.3698	$66.37	$66.35	$66.40
Purchase #5	$113.53	12.862%	$128.1322	$128.13	$128.15	$128.10
Purchase #6	$162.43	11.862%	$181.6974	$181.70	$181.70	$181.70
Purchase #7	$27.47	8.815%	$29.8915	$29.89	$29.90	$29.90
7 purchase totals =	$900.98		$994.0143	$994.01	$994.05	$994.00