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	$69.59	4.339%	$72.6095	$72.61	$72.60	$72.60
Purchase #2	$27.94	10.561%	$30.8907	$30.89	$30.90	$30.90
Purchase #3	$148.69	7.356%	$159.6276	$159.63	$159.65	$159.60
Purchase #4	$114.60	8.107%	$123.8906	$123.89	$123.90	$123.90
Purchase #5	$86.65	10.471%	$95.7231	$95.72	$95.70	$95.70
Purchase #6	$123.65	4.757%	$129.532	$129.53	$129.55	$129.50
Purchase #7	$51.56	5.856%	$54.5794	$54.58	$54.60	$54.60
7 purchase totals =	$622.68		$666.8529	$666.85	$666.90	$666.80