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	$62.67	5.307%	$65.9959	$66.00	$66.00	$66.00
Purchase #2	$201.66	4.410%	$210.5532	$210.55	$210.55	$210.60
Purchase #3	$150.40	7.237%	$161.2844	$161.28	$161.30	$161.30
Purchase #4	$20.86	3.392%	$21.5676	$21.57	$21.55	$21.60
Purchase #5	$17.82	8.851%	$19.3972	$19.40	$19.40	$19.40
Purchase #6	$165.80	3.629%	$171.8169	$171.82	$171.80	$171.80
Purchase #7	$185.32	5.811%	$196.0889	$196.09	$196.10	$196.10
7 purchase totals =	$804.53		$846.7041	$846.71	$846.70	$846.80