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	$168.78	6.874%	$180.3819	$180.38	$180.40	$180.40
Purchase #2	$52.78	3.311%	$54.5275	$54.53	$54.55	$54.50
Purchase #3	$169.80	11.296%	$188.9806	$188.98	$189.00	$189.00
Purchase #4	$127.95	3.211%	$132.0585	$132.06	$132.05	$132.10
Purchase #5	$132.66	8.134%	$143.4506	$143.45	$143.45	$143.50
Purchase #6	$17.51	5.592%	$18.4892	$18.49	$18.50	$18.50
Purchase #7	$100.33	11.646%	$112.0144	$112.01	$112.00	$112.00
7 purchase totals =	$769.81		$829.9027	$829.90	$829.95	$830.00