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	$245.35	7.788%	$264.4579	$264.46	$264.45	$264.50
Purchase #2	$240.85	5.414%	$253.8896	$253.89	$253.90	$253.90
Purchase #3	$117.70	5.264%	$123.8957	$123.90	$123.90	$123.90
Purchase #4	$108.83	13.198%	$123.1934	$123.19	$123.20	$123.20
Purchase #5	$107.61	3.744%	$111.6389	$111.64	$111.65	$111.60
Purchase #6	$49.53	7.116%	$53.0546	$53.05	$53.05	$53.10
Purchase #7	$97.70	3.462%	$101.0824	$101.08	$101.10	$101.10
7 purchase totals =	$967.57		$1,031.2125	$1,031.21	$1,031.25	$1,031.30