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	$51.56	10.334%	$56.8882	$56.89	$56.90	$56.90
Purchase #2	$59.28	10.756%	$65.6562	$65.66	$65.65	$65.70
Purchase #3	$59.79	11.314%	$66.5546	$66.55	$66.55	$66.60
Purchase #4	$95.52	7.692%	$102.8674	$102.87	$102.85	$102.90
Purchase #5	$28.87	6.464%	$30.7362	$30.74	$30.75	$30.70
Purchase #6	$190.82	13.207%	$216.0216	$216.02	$216.00	$216.00
Purchase #7	$39.45	3.785%	$40.9432	$40.94	$40.95	$40.90
7 purchase totals =	$525.29		$579.6674	$579.67	$579.65	$579.70