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	$131.86	9.141%	$143.9133	$143.91	$143.90	$143.90
Purchase #2	$198.29	9.740%	$217.6034	$217.60	$217.60	$217.60
Purchase #3	$194.28	4.836%	$203.6754	$203.68	$203.70	$203.70
Purchase #4	$155.49	13.776%	$176.9103	$176.91	$176.90	$176.90
Purchase #5	$163.87	5.192%	$172.3781	$172.38	$172.40	$172.40
Purchase #6	$109.40	8.316%	$118.4977	$118.50	$118.50	$118.50
Purchase #7	$54.70	3.116%	$56.4045	$56.40	$56.40	$56.40
7 purchase totals =	$1,007.89		$1,089.3827	$1,089.38	$1,089.40	$1,089.40