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	$38.53	10.682%	$42.6458	$42.65	$42.65	$42.60
Purchase #2	$59.48	13.456%	$67.4836	$67.48	$67.50	$67.50
Purchase #3	$71.28	13.280%	$80.746	$80.75	$80.75	$80.70
Purchase #4	$137.45	3.561%	$142.3446	$142.34	$142.35	$142.30
Purchase #5	$241.43	6.646%	$257.4754	$257.48	$257.50	$257.50
Purchase #6	$94.74	3.291%	$97.8579	$97.86	$97.85	$97.90
Purchase #7	$38.85	4.186%	$40.4763	$40.48	$40.50	$40.50
7 purchase totals =	$681.76		$729.0296	$729.04	$729.10	$729.00