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	$43.42	4.259%	$45.2693	$45.27	$45.25	$45.30
Purchase #2	$20.90	3.136%	$21.5554	$21.56	$21.55	$21.60
Purchase #3	$205.58	5.690%	$217.2775	$217.28	$217.30	$217.30
Purchase #4	$118.86	11.208%	$132.1818	$132.18	$132.20	$132.20
Purchase #5	$18.57	5.723%	$19.6328	$19.63	$19.65	$19.60
Purchase #6	$42.28	8.272%	$45.7774	$45.78	$45.80	$45.80
Purchase #7	$120.77	13.682%	$137.2938	$137.29	$137.30	$137.30
7 purchase totals =	$570.38		$618.9880	$618.99	$619.05	$619.10