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	$18.95	4.851%	$19.8693	$19.87	$19.85	$19.90
Purchase #2	$78.95	7.516%	$84.8839	$84.88	$84.90	$84.90
Purchase #3	$39.94	9.396%	$43.6928	$43.69	$43.70	$43.70
Purchase #4	$120.39	9.397%	$131.703	$131.70	$131.70	$131.70
Purchase #5	$40.90	11.600%	$45.6444	$45.64	$45.65	$45.60
Purchase #6	$40.88	6.139%	$43.3896	$43.39	$43.40	$43.40
Purchase #7	$217.36	3.330%	$224.5981	$224.60	$224.60	$224.60
7 purchase totals =	$557.37		$593.7811	$593.77	$593.80	$593.80