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	$238.59	8.794%	$259.5716	$259.57	$259.55	$259.60
Purchase #2	$20.35	4.321%	$21.2293	$21.23	$21.25	$21.20
Purchase #3	$198.86	13.189%	$225.0876	$225.09	$225.10	$225.10
Purchase #4	$95.64	10.654%	$105.8295	$105.83	$105.85	$105.80
Purchase #5	$53.65	6.732%	$57.2617	$57.26	$57.25	$57.30
Purchase #6	$49.90	13.760%	$56.7662	$56.77	$56.75	$56.80
Purchase #7	$115.63	6.683%	$123.3576	$123.36	$123.35	$123.40
7 purchase totals =	$772.62		$849.1035	$849.11	$849.10	$849.20