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	$244.54	6.531%	$260.5109	$260.51	$260.50	$260.50
Purchase #2	$36.53	5.862%	$38.6714	$38.67	$38.65	$38.70
Purchase #3	$57.34	7.837%	$61.8337	$61.83	$61.85	$61.80
Purchase #4	$234.59	11.523%	$261.6218	$261.62	$261.60	$261.60
Purchase #5	$17.71	10.622%	$19.5912	$19.59	$19.60	$19.60
Purchase #6	$92.45	3.472%	$95.6599	$95.66	$95.65	$95.70
Purchase #7	$89.62	13.406%	$101.6345	$101.63	$101.65	$101.60
7 purchase totals =	$772.78		$839.5234	$839.51	$839.50	$839.50