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	$151.47	5.274%	$159.4585	$159.46	$159.45	$159.50
Purchase #2	$182.58	6.564%	$194.5646	$194.56	$194.55	$194.60
Purchase #3	$92.38	8.699%	$100.4161	$100.42	$100.40	$100.40
Purchase #4	$138.66	5.752%	$146.6357	$146.64	$146.65	$146.60
Purchase #5	$115.51	10.810%	$127.9966	$128.00	$128.00	$128.00
Purchase #6	$83.87	3.664%	$86.943	$86.94	$86.95	$86.90
Purchase #7	$144.77	10.234%	$159.5858	$159.59	$159.60	$159.60
7 purchase totals =	$909.24		$975.6003	$975.61	$975.60	$975.60