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	$65.71	5.418%	$69.2702	$69.27	$69.25	$69.30
Purchase #2	$34.63	11.385%	$38.5726	$38.57	$38.55	$38.60
Purchase #3	$63.80	4.281%	$66.5313	$66.53	$66.55	$66.50
Purchase #4	$206.50	7.443%	$221.8698	$221.87	$221.85	$221.90
Purchase #5	$61.94	6.581%	$66.0163	$66.02	$66.00	$66.00
Purchase #6	$114.85	7.489%	$123.4511	$123.45	$123.45	$123.50
Purchase #7	$89.74	11.516%	$100.0745	$100.07	$100.05	$100.10
7 purchase totals =	$637.17		$685.7858	$685.78	$685.70	$685.90