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	$97.26	8.303%	$105.3355	$105.34	$105.35	$105.30
Purchase #2	$140.99	12.630%	$158.797	$158.80	$158.80	$158.80
Purchase #3	$48.31	13.178%	$54.6763	$54.68	$54.70	$54.70
Purchase #4	$17.57	8.623%	$19.0851	$19.09	$19.10	$19.10
Purchase #5	$7.55	4.307%	$7.8752	$7.88	$7.90	$7.90
Purchase #6	$86.58	4.105%	$90.1341	$90.13	$90.15	$90.10
Purchase #7	$86.78	10.869%	$96.2121	$96.21	$96.20	$96.20
7 purchase totals =	$485.04		$532.1153	$532.13	$532.20	$532.10