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	$160.57	6.539%	$171.0697	$171.07	$171.05	$171.10
Purchase #2	$48.75	13.426%	$55.2952	$55.30	$55.30	$55.30
Purchase #3	$162.80	5.333%	$171.4821	$171.48	$171.50	$171.50
Purchase #4	$155.49	11.484%	$173.3465	$173.35	$173.35	$173.30
Purchase #5	$14.93	4.338%	$15.5777	$15.58	$15.60	$15.60
Purchase #6	$112.76	5.231%	$118.6585	$118.66	$118.65	$118.70
Purchase #7	$90.61	10.588%	$100.2038	$100.20	$100.20	$100.20
7 purchase totals =	$745.91		$805.6335	$805.64	$805.65	$805.70