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	$10.71	8.391%	$11.6087	$11.61	$11.60	$11.60
Purchase #2	$38.33	12.434%	$43.096	$43.10	$43.10	$43.10
Purchase #3	$208.42	7.113%	$223.2449	$223.24	$223.25	$223.20
Purchase #4	$62.87	5.306%	$66.2059	$66.21	$66.20	$66.20
Purchase #5	$156.87	10.533%	$173.3931	$173.39	$173.40	$173.40
Purchase #6	$31.79	5.660%	$33.5893	$33.59	$33.60	$33.60
Purchase #7	$123.90	4.438%	$129.3987	$129.40	$129.40	$129.40
7 purchase totals =	$632.89		$680.5366	$680.54	$680.55	$680.50