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	$32.88	5.788%	$34.7831	$34.78	$34.80	$34.80
Purchase #2	$81.97	13.840%	$93.3146	$93.31	$93.30	$93.30
Purchase #3	$128.34	3.180%	$132.4212	$132.42	$132.40	$132.40
Purchase #4	$19.59	10.522%	$21.6513	$21.65	$21.65	$21.70
Purchase #5	$85.72	5.798%	$90.69	$90.69	$90.70	$90.70
Purchase #6	$5.91	12.603%	$6.6548	$6.65	$6.65	$6.70
Purchase #7	$199.30	11.565%	$222.349	$222.35	$222.35	$222.30
7 purchase totals =	$553.71		$601.8640	$601.85	$601.85	$601.90