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	$38.97	11.422%	$43.4212	$43.42	$43.40	$43.40
Purchase #2	$166.83	3.412%	$172.5222	$172.52	$172.50	$172.50
Purchase #3	$159.71	13.598%	$181.4274	$181.43	$181.45	$181.40
Purchase #4	$105.98	6.218%	$112.5698	$112.57	$112.55	$112.60
Purchase #5	$165.57	5.638%	$174.9048	$174.90	$174.90	$174.90
Purchase #6	$151.74	5.315%	$159.805	$159.81	$159.80	$159.80
Purchase #7	$40.38	11.141%	$44.8787	$44.88	$44.90	$44.90
7 purchase totals =	$829.18		$889.5291	$889.53	$889.50	$889.50