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	$228.59	11.679%	$255.287	$255.29	$255.30	$255.30
Purchase #2	$170.89	10.536%	$188.895	$188.90	$188.90	$188.90
Purchase #3	$152.82	4.298%	$159.3882	$159.39	$159.40	$159.40
Purchase #4	$60.94	9.458%	$66.7037	$66.70	$66.70	$66.70
Purchase #5	$90.82	10.201%	$100.0845	$100.08	$100.10	$100.10
Purchase #6	$112.78	7.507%	$121.2464	$121.25	$121.25	$121.20
Purchase #7	$5.59	10.481%	$6.1759	$6.18	$6.20	$6.20
7 purchase totals =	$822.43		$897.7807	$897.79	$897.85	$897.80