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	$208.35	11.191%	$231.6664	$231.67	$231.65	$231.70
Purchase #2	$119.28	11.858%	$133.4242	$133.42	$133.40	$133.40
Purchase #3	$111.75	10.533%	$123.5206	$123.52	$123.50	$123.50
Purchase #4	$123.42	7.191%	$132.2951	$132.30	$132.30	$132.30
Purchase #5	$137.44	11.159%	$152.7769	$152.78	$152.80	$152.80
Purchase #6	$15.40	3.651%	$15.9623	$15.96	$15.95	$16.00
Purchase #7	$29.45	12.822%	$33.2261	$33.23	$33.25	$33.20
7 purchase totals =	$745.09		$822.8716	$822.88	$822.85	$822.90