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	$71.57	13.637%	$81.33	$81.33	$81.35	$81.30
Purchase #2	$210.61	3.561%	$218.1098	$218.11	$218.10	$218.10
Purchase #3	$246.69	3.575%	$255.5092	$255.51	$255.50	$255.50
Purchase #4	$235.59	13.214%	$266.7209	$266.72	$266.70	$266.70
Purchase #5	$126.48	12.422%	$142.1913	$142.19	$142.20	$142.20
Purchase #6	$102.32	7.102%	$109.5868	$109.59	$109.60	$109.60
Purchase #7	$62.77	6.458%	$66.8237	$66.82	$66.80	$66.80
7 purchase totals =	$1,056.03		$1,140.2717	$1,140.27	$1,140.25	$1,140.20