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	$75.93	12.581%	$85.4828	$85.48	$85.50	$85.50
Purchase #2	$12.47	11.328%	$13.8826	$13.88	$13.90	$13.90
Purchase #3	$236.78	12.122%	$265.4825	$265.48	$265.50	$265.50
Purchase #4	$31.54	10.574%	$34.875	$34.88	$34.90	$34.90
Purchase #5	$9.85	8.817%	$10.7185	$10.72	$10.70	$10.70
Purchase #6	$242.86	3.185%	$250.5951	$250.60	$250.60	$250.60
Purchase #7	$100.31	8.129%	$108.4642	$108.46	$108.45	$108.50
7 purchase totals =	$709.74		$769.5007	$769.50	$769.55	$769.60