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	$49.54	12.685%	$55.8241	$55.82	$55.80	$55.80
Purchase #2	$24.76	11.667%	$27.6487	$27.65	$27.65	$27.60
Purchase #3	$75.29	13.839%	$85.7094	$85.71	$85.70	$85.70
Purchase #4	$126.32	4.135%	$131.5433	$131.54	$131.55	$131.50
Purchase #5	$113.27	13.351%	$128.3927	$128.39	$128.40	$128.40
Purchase #6	$138.89	3.598%	$143.8873	$143.89	$143.90	$143.90
Purchase #7	$230.30	13.677%	$261.7981	$261.80	$261.80	$261.80
7 purchase totals =	$758.37		$834.8036	$834.80	$834.80	$834.70