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	$53.60	3.495%	$55.4733	$55.47	$55.45	$55.50
Purchase #2	$229.54	5.697%	$242.6169	$242.62	$242.60	$242.60
Purchase #3	$26.44	3.709%	$27.4207	$27.42	$27.40	$27.40
Purchase #4	$27.85	4.222%	$29.0258	$29.03	$29.05	$29.00
Purchase #5	$116.78	12.601%	$131.4954	$131.50	$131.50	$131.50
Purchase #6	$11.25	6.548%	$11.9867	$11.99	$12.00	$12.00
Purchase #7	$111.74	10.529%	$123.5051	$123.51	$123.50	$123.50
7 purchase totals =	$577.20		$621.5239	$621.54	$621.50	$621.50