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	$139.47	9.358%	$152.5216	$152.52	$152.50	$152.50
Purchase #2	$241.71	9.465%	$264.5879	$264.59	$264.60	$264.60
Purchase #3	$199.88	7.764%	$215.3987	$215.40	$215.40	$215.40
Purchase #4	$85.64	5.538%	$90.3827	$90.38	$90.40	$90.40
Purchase #5	$47.71	7.634%	$51.3522	$51.35	$51.35	$51.40
Purchase #6	$45.54	7.836%	$49.1085	$49.11	$49.10	$49.10
Purchase #7	$57.43	10.492%	$63.4556	$63.46	$63.45	$63.50
7 purchase totals =	$817.38		$886.8072	$886.81	$886.80	$886.90