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	$111.94	6.219%	$118.9015	$118.90	$118.90	$118.90
Purchase #2	$135.69	6.131%	$144.0092	$144.01	$144.00	$144.00
Purchase #3	$8.77	11.773%	$9.8025	$9.80	$9.80	$9.80
Purchase #4	$133.53	13.519%	$151.5819	$151.58	$151.60	$151.60
Purchase #5	$124.47	13.790%	$141.6344	$141.63	$141.65	$141.60
Purchase #6	$82.78	9.835%	$90.9214	$90.92	$90.90	$90.90
Purchase #7	$28.83	8.845%	$31.38	$31.38	$31.40	$31.40
7 purchase totals =	$626.01		$688.2309	$688.22	$688.25	$688.20