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	$62.91	7.451%	$67.5974	$67.60	$67.60	$67.60
Purchase #2	$66.84	8.282%	$72.3757	$72.38	$72.40	$72.40
Purchase #3	$33.71	11.342%	$37.5334	$37.53	$37.55	$37.50
Purchase #4	$110.75	8.252%	$119.8891	$119.89	$119.90	$119.90
Purchase #5	$46.48	10.309%	$51.2716	$51.27	$51.25	$51.30
Purchase #6	$183.65	7.326%	$197.1042	$197.10	$197.10	$197.10
Purchase #7	$83.46	13.833%	$95.005	$95.01	$95.00	$95.00
7 purchase totals =	$587.80		$640.7764	$640.78	$640.80	$640.80