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	$13.67	12.661%	$15.4008	$15.40	$15.40	$15.40
Purchase #2	$20.78	8.521%	$22.5507	$22.55	$22.55	$22.60
Purchase #3	$78.40	10.636%	$86.7386	$86.74	$86.75	$86.70
Purchase #4	$142.59	11.301%	$158.7041	$158.70	$158.70	$158.70
Purchase #5	$22.26	12.337%	$25.0062	$25.01	$25.00	$25.00
Purchase #6	$72.44	8.302%	$78.454	$78.45	$78.45	$78.50
Purchase #7	$74.33	12.520%	$83.6361	$83.64	$83.65	$83.60
7 purchase totals =	$424.47		$470.4905	$470.49	$470.50	$470.50