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	$122.51	8.692%	$133.1586	$133.16	$133.15	$133.20
Purchase #2	$111.92	9.459%	$122.5065	$122.51	$122.50	$122.50
Purchase #3	$52.93	8.309%	$57.328	$57.33	$57.35	$57.30
Purchase #4	$115.87	5.186%	$121.879	$121.88	$121.90	$121.90
Purchase #5	$108.53	13.482%	$123.162	$123.16	$123.15	$123.20
Purchase #6	$159.27	6.510%	$169.6385	$169.64	$169.65	$169.60
Purchase #7	$226.86	12.665%	$255.5918	$255.59	$255.60	$255.60
7 purchase totals =	$897.89		$983.2644	$983.27	$983.30	$983.30