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	$108.88	13.116%	$123.1607	$123.16	$123.15	$123.20
Purchase #2	$19.88	3.544%	$20.5845	$20.58	$20.60	$20.60
Purchase #3	$80.71	8.429%	$87.513	$87.51	$87.50	$87.50
Purchase #4	$54.36	4.103%	$56.5904	$56.59	$56.60	$56.60
Purchase #5	$49.52	10.618%	$54.778	$54.78	$54.80	$54.80
Purchase #6	$209.82	8.770%	$228.2212	$228.22	$228.20	$228.20
Purchase #7	$71.28	8.599%	$77.4094	$77.41	$77.40	$77.40
7 purchase totals =	$594.45		$648.2572	$648.25	$648.25	$648.30