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	$28.89	9.540%	$31.6461	$31.65	$31.65	$31.60
Purchase #2	$233.87	9.382%	$255.8117	$255.81	$255.80	$255.80
Purchase #3	$181.86	4.742%	$190.4838	$190.48	$190.50	$190.50
Purchase #4	$158.34	11.584%	$176.6821	$176.68	$176.70	$176.70
Purchase #5	$85.98	13.723%	$97.779	$97.78	$97.80	$97.80
Purchase #6	$83.53	7.713%	$89.9727	$89.97	$89.95	$90.00
Purchase #7	$219.62	5.382%	$231.4399	$231.44	$231.45	$231.40
7 purchase totals =	$992.09		$1,073.8153	$1,073.81	$1,073.85	$1,073.80