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	$132.88	4.311%	$138.6085	$138.61	$138.60	$138.60
Purchase #2	$237.46	6.600%	$253.1324	$253.13	$253.15	$253.10
Purchase #3	$248.47	6.824%	$265.4256	$265.43	$265.45	$265.40
Purchase #4	$41.90	3.796%	$43.4905	$43.49	$43.50	$43.50
Purchase #5	$32.43	12.198%	$36.3858	$36.39	$36.40	$36.40
Purchase #6	$224.83	10.267%	$247.9133	$247.91	$247.90	$247.90
Purchase #7	$50.91	9.221%	$55.6044	$55.60	$55.60	$55.60
7 purchase totals =	$968.88		$1,040.5605	$1,040.56	$1,040.60	$1,040.50