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	$74.79	9.540%	$81.925	$81.93	$81.95	$81.90
Purchase #2	$28.72	3.591%	$29.7513	$29.75	$29.75	$29.80
Purchase #3	$246.79	8.536%	$267.856	$267.86	$267.85	$267.90
Purchase #4	$151.32	11.324%	$168.4555	$168.46	$168.45	$168.50
Purchase #5	$116.33	10.235%	$128.2364	$128.24	$128.25	$128.20
Purchase #6	$117.57	9.581%	$128.8344	$128.83	$128.85	$128.80
Purchase #7	$51.95	4.548%	$54.3127	$54.31	$54.30	$54.30
7 purchase totals =	$787.47		$859.3713	$859.38	$859.40	$859.40