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	$239.83	11.585%	$267.6143	$267.61	$267.60	$267.60
Purchase #2	$52.38	13.322%	$59.3581	$59.36	$59.35	$59.40
Purchase #3	$104.79	4.693%	$109.7078	$109.71	$109.70	$109.70
Purchase #4	$131.29	9.334%	$143.5446	$143.54	$143.55	$143.50
Purchase #5	$60.42	13.696%	$68.6951	$68.70	$68.70	$68.70
Purchase #6	$13.60	12.572%	$15.3098	$15.31	$15.30	$15.30
Purchase #7	$233.89	6.253%	$248.5151	$248.52	$248.50	$248.50
7 purchase totals =	$836.20		$912.7448	$912.75	$912.70	$912.70