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	$57.89	12.592%	$65.1795	$65.18	$65.20	$65.20
Purchase #2	$49.38	11.811%	$55.2123	$55.21	$55.20	$55.20
Purchase #3	$95.26	6.642%	$101.5872	$101.59	$101.60	$101.60
Purchase #4	$133.99	3.181%	$138.2522	$138.25	$138.25	$138.30
Purchase #5	$161.33	7.602%	$173.5943	$173.59	$173.60	$173.60
Purchase #6	$183.43	13.680%	$208.5232	$208.52	$208.50	$208.50
Purchase #7	$68.92	13.296%	$78.0836	$78.08	$78.10	$78.10
7 purchase totals =	$750.20		$820.4323	$820.42	$820.45	$820.50