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	$246.96	13.559%	$280.4453	$280.45	$280.45	$280.40
Purchase #2	$205.36	6.719%	$219.1581	$219.16	$219.15	$219.20
Purchase #3	$234.88	9.368%	$256.8836	$256.88	$256.90	$256.90
Purchase #4	$11.93	9.840%	$13.1039	$13.10	$13.10	$13.10
Purchase #5	$82.46	6.356%	$87.7012	$87.70	$87.70	$87.70
Purchase #6	$143.33	10.581%	$158.4957	$158.50	$158.50	$158.50
Purchase #7	$22.97	10.814%	$25.454	$25.45	$25.45	$25.50
7 purchase totals =	$947.89		$1,041.2418	$1,041.24	$1,041.25	$1,041.30