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	$69.32	13.211%	$78.4779	$78.48	$78.50	$78.50
Purchase #2	$229.33	12.404%	$257.7761	$257.78	$257.80	$257.80
Purchase #3	$72.89	5.522%	$76.915	$76.92	$76.90	$76.90
Purchase #4	$85.25	12.566%	$95.9625	$95.96	$95.95	$96.00
Purchase #5	$40.58	12.523%	$45.6618	$45.66	$45.65	$45.70
Purchase #6	$30.42	4.568%	$31.8096	$31.81	$31.80	$31.80
Purchase #7	$187.48	13.845%	$213.4366	$213.44	$213.45	$213.40
7 purchase totals =	$715.27		$800.0395	$800.05	$800.05	$800.10