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	$171.90	12.115%	$192.7257	$192.73	$192.75	$192.70
Purchase #2	$175.93	12.832%	$198.5053	$198.51	$198.50	$198.50
Purchase #3	$136.46	7.564%	$146.7818	$146.78	$146.80	$146.80
Purchase #4	$51.38	11.690%	$57.3863	$57.39	$57.40	$57.40
Purchase #5	$67.68	7.289%	$72.6132	$72.61	$72.60	$72.60
Purchase #6	$195.51	10.693%	$216.4159	$216.42	$216.40	$216.40
Purchase #7	$43.47	12.323%	$48.8268	$48.83	$48.85	$48.80
7 purchase totals =	$842.33		$933.2550	$933.27	$933.30	$933.20