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	$78.25	6.668%	$83.4677	$83.47	$83.45	$83.50
Purchase #2	$93.34	12.423%	$104.9356	$104.94	$104.95	$104.90
Purchase #3	$235.70	10.855%	$261.2852	$261.29	$261.30	$261.30
Purchase #4	$166.64	12.246%	$187.0467	$187.05	$187.05	$187.00
Purchase #5	$19.48	8.233%	$21.0838	$21.08	$21.10	$21.10
Purchase #6	$109.92	6.848%	$117.4473	$117.45	$117.45	$117.40
Purchase #7	$111.83	10.853%	$123.9669	$123.97	$123.95	$124.00
7 purchase totals =	$815.16		$899.2332	$899.25	$899.25	$899.20