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	$103.53	13.858%	$117.8772	$117.88	$117.90	$117.90
Purchase #2	$170.60	12.808%	$192.4504	$192.45	$192.45	$192.50
Purchase #3	$89.34	12.407%	$100.4244	$100.42	$100.40	$100.40
Purchase #4	$33.95	6.146%	$36.0366	$36.04	$36.05	$36.00
Purchase #5	$95.46	4.349%	$99.6116	$99.61	$99.60	$99.60
Purchase #6	$13.96	5.706%	$14.7566	$14.76	$14.75	$14.80
Purchase #7	$73.87	6.662%	$78.7912	$78.79	$78.80	$78.80
7 purchase totals =	$580.71		$639.9480	$639.95	$639.95	$640.00