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	$38.35	9.496%	$41.9917	$41.99	$42.00	$42.00
Purchase #2	$137.47	5.329%	$144.7958	$144.80	$144.80	$144.80
Purchase #3	$206.78	4.401%	$215.8804	$215.88	$215.90	$215.90
Purchase #4	$47.88	7.637%	$51.5366	$51.54	$51.55	$51.50
Purchase #5	$35.47	11.610%	$39.5881	$39.59	$39.60	$39.60
Purchase #6	$20.44	6.622%	$21.7935	$21.79	$21.80	$21.80
Purchase #7	$81.76	13.411%	$92.7248	$92.72	$92.70	$92.70
7 purchase totals =	$568.15		$608.3109	$608.31	$608.35	$608.30