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	$41.72	10.124%	$45.9437	$45.94	$45.95	$45.90
Purchase #2	$49.57	10.553%	$54.8011	$54.80	$54.80	$54.80
Purchase #3	$25.78	13.342%	$29.2196	$29.22	$29.20	$29.20
Purchase #4	$244.79	8.511%	$265.6241	$265.62	$265.60	$265.60
Purchase #5	$128.50	6.218%	$136.4901	$136.49	$136.50	$136.50
Purchase #6	$56.50	12.229%	$63.4094	$63.41	$63.40	$63.40
Purchase #7	$30.36	10.242%	$33.4695	$33.47	$33.45	$33.50
7 purchase totals =	$577.22		$628.9575	$628.95	$628.90	$628.90