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	$47.91	13.671%	$54.4598	$54.46	$54.45	$54.50
Purchase #2	$16.31	13.329%	$18.484	$18.48	$18.50	$18.50
Purchase #3	$123.85	13.240%	$140.2477	$140.25	$140.25	$140.20
Purchase #4	$239.41	6.718%	$255.4936	$255.49	$255.50	$255.50
Purchase #5	$43.79	9.349%	$47.8839	$47.88	$47.90	$47.90
Purchase #6	$37.83	5.493%	$39.908	$39.91	$39.90	$39.90
Purchase #7	$130.56	10.555%	$144.3406	$144.34	$144.35	$144.30
7 purchase totals =	$639.66		$700.8176	$700.81	$700.85	$700.80