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	$120.82	3.870%	$125.4957	$125.50	$125.50	$125.50
Purchase #2	$230.69	10.788%	$255.5768	$255.58	$255.60	$255.60
Purchase #3	$6.87	8.509%	$7.4546	$7.45	$7.45	$7.50
Purchase #4	$39.82	11.814%	$44.5243	$44.52	$44.50	$44.50
Purchase #5	$112.33	12.523%	$126.3971	$126.40	$126.40	$126.40
Purchase #6	$93.52	10.491%	$103.3312	$103.33	$103.35	$103.30
Purchase #7	$208.75	6.393%	$222.0954	$222.10	$222.10	$222.10
7 purchase totals =	$812.80		$884.8751	$884.88	$884.90	$884.90