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	$121.42	13.727%	$138.0873	$138.09	$138.10	$138.10
Purchase #2	$132.46	5.625%	$139.9109	$139.91	$139.90	$139.90
Purchase #3	$163.62	7.389%	$175.7099	$175.71	$175.70	$175.70
Purchase #4	$70.50	11.866%	$78.8655	$78.87	$78.85	$78.90
Purchase #5	$228.85	13.809%	$260.4519	$260.45	$260.45	$260.50
Purchase #6	$126.87	4.288%	$132.3102	$132.31	$132.30	$132.30
Purchase #7	$201.59	11.855%	$225.4885	$225.49	$225.50	$225.50
7 purchase totals =	$1,045.31		$1,150.8242	$1,150.83	$1,150.80	$1,150.90