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	$206.81	12.789%	$233.2589	$233.26	$233.25	$233.30
Purchase #2	$83.70	7.527%	$90.0001	$90.00	$90.00	$90.00
Purchase #3	$118.65	5.233%	$124.859	$124.86	$124.85	$124.90
Purchase #4	$11.56	7.845%	$12.4669	$12.47	$12.45	$12.50
Purchase #5	$113.43	5.796%	$120.0044	$120.00	$120.00	$120.00
Purchase #6	$152.69	10.663%	$168.9713	$168.97	$168.95	$169.00
Purchase #7	$74.71	9.677%	$81.9397	$81.94	$81.95	$81.90
7 purchase totals =	$761.55		$831.5003	$831.50	$831.45	$831.60