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	$247.46	13.357%	$280.5132	$280.51	$280.50	$280.50
Purchase #2	$111.54	7.361%	$119.7505	$119.75	$119.75	$119.80
Purchase #3	$173.65	3.339%	$179.4482	$179.45	$179.45	$179.40
Purchase #4	$61.31	11.778%	$68.5311	$68.53	$68.55	$68.50
Purchase #5	$16.42	12.365%	$18.4503	$18.45	$18.45	$18.50
Purchase #6	$205.68	9.635%	$225.4973	$225.50	$225.50	$225.50
Purchase #7	$232.98	10.179%	$256.695	$256.70	$256.70	$256.70
7 purchase totals =	$1,049.04		$1,148.8856	$1,148.89	$1,148.90	$1,148.90