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	$128.32	12.285%	$144.0841	$144.08	$144.10	$144.10
Purchase #2	$182.37	12.413%	$205.0076	$205.01	$205.00	$205.00
Purchase #3	$167.53	9.773%	$183.9027	$183.90	$183.90	$183.90
Purchase #4	$62.46	6.800%	$66.7073	$66.71	$66.70	$66.70
Purchase #5	$157.98	8.808%	$171.8949	$171.89	$171.90	$171.90
Purchase #6	$35.76	8.757%	$38.8915	$38.89	$38.90	$38.90
Purchase #7	$143.42	5.631%	$151.496	$151.50	$151.50	$151.50
7 purchase totals =	$877.84		$961.9841	$961.98	$962.00	$962.00