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	$120.57	9.715%	$132.2834	$132.28	$132.30	$132.30
Purchase #2	$97.49	11.548%	$108.7481	$108.75	$108.75	$108.70
Purchase #3	$47.43	10.692%	$52.5012	$52.50	$52.50	$52.50
Purchase #4	$173.72	8.604%	$188.6669	$188.67	$188.65	$188.70
Purchase #5	$74.52	10.670%	$82.4713	$82.47	$82.45	$82.50
Purchase #6	$43.60	11.487%	$48.6083	$48.61	$48.60	$48.60
Purchase #7	$199.32	11.768%	$222.776	$222.78	$222.80	$222.80
7 purchase totals =	$756.65		$836.0552	$836.06	$836.05	$836.10