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	$232.72	9.582%	$255.0192	$255.02	$255.00	$255.00
Purchase #2	$112.31	3.743%	$116.5138	$116.51	$116.50	$116.50
Purchase #3	$121.71	9.233%	$132.9475	$132.95	$132.95	$132.90
Purchase #4	$98.93	10.631%	$109.4472	$109.45	$109.45	$109.40
Purchase #5	$234.70	13.515%	$266.4197	$266.42	$266.40	$266.40
Purchase #6	$8.40	6.575%	$8.9523	$8.95	$8.95	$9.00
Purchase #7	$204.70	8.792%	$222.6972	$222.70	$222.70	$222.70
7 purchase totals =	$1,013.47		$1,111.9969	$1,112.00	$1,111.95	$1,111.90