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	$50.25	13.159%	$56.8624	$56.86	$56.85	$56.90
Purchase #2	$169.33	11.857%	$189.4075	$189.41	$189.40	$189.40
Purchase #3	$110.83	11.112%	$123.1454	$123.15	$123.15	$123.10
Purchase #4	$76.51	12.198%	$85.8427	$85.84	$85.85	$85.80
Purchase #5	$193.82	10.837%	$214.8243	$214.82	$214.80	$214.80
Purchase #6	$77.82	12.524%	$87.5662	$87.57	$87.55	$87.60
Purchase #7	$143.87	6.749%	$153.5798	$153.58	$153.60	$153.60
7 purchase totals =	$822.43		$911.2283	$911.23	$911.20	$911.20