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	$41.78	3.635%	$43.2987	$43.30	$43.30	$43.30
Purchase #2	$31.40	5.661%	$33.1776	$33.18	$33.20	$33.20
Purchase #3	$52.71	4.384%	$55.0208	$55.02	$55.00	$55.00
Purchase #4	$94.92	9.810%	$104.2317	$104.23	$104.25	$104.20
Purchase #5	$49.75	5.369%	$52.4211	$52.42	$52.40	$52.40
Purchase #6	$103.56	4.719%	$108.447	$108.45	$108.45	$108.40
Purchase #7	$100.95	11.517%	$112.5764	$112.58	$112.60	$112.60
7 purchase totals =	$475.07		$509.1733	$509.18	$509.20	$509.10