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	$64.73	3.269%	$66.846	$66.85	$66.85	$66.80
Purchase #2	$29.75	6.342%	$31.6367	$31.64	$31.65	$31.60
Purchase #3	$58.70	6.443%	$62.482	$62.48	$62.50	$62.50
Purchase #4	$163.45	9.853%	$179.5547	$179.55	$179.55	$179.60
Purchase #5	$192.77	9.210%	$210.5241	$210.52	$210.50	$210.50
Purchase #6	$119.51	3.491%	$123.6821	$123.68	$123.70	$123.70
Purchase #7	$152.56	10.437%	$168.4827	$168.48	$168.50	$168.50
7 purchase totals =	$781.47		$843.2083	$843.20	$843.25	$843.20