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	$80.92	11.724%	$90.4071	$90.41	$90.40	$90.40
Purchase #2	$103.94	8.188%	$112.4506	$112.45	$112.45	$112.50
Purchase #3	$80.87	12.126%	$90.6763	$90.68	$90.70	$90.70
Purchase #4	$135.58	9.323%	$148.2201	$148.22	$148.20	$148.20
Purchase #5	$41.50	4.262%	$43.2687	$43.27	$43.25	$43.30
Purchase #6	$5.54	5.255%	$5.8311	$5.83	$5.85	$5.80
Purchase #7	$62.62	9.752%	$68.7267	$68.73	$68.75	$68.70
7 purchase totals =	$510.97		$559.5806	$559.59	$559.60	$559.60