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	$244.67	6.226%	$259.9032	$259.90	$259.90	$259.90
Purchase #2	$201.25	13.808%	$229.0386	$229.04	$229.05	$229.00
Purchase #3	$245.66	8.637%	$266.8777	$266.88	$266.90	$266.90
Purchase #4	$102.29	9.301%	$111.804	$111.80	$111.80	$111.80
Purchase #5	$12.89	7.253%	$13.8249	$13.82	$13.80	$13.80
Purchase #6	$20.92	12.425%	$23.5193	$23.52	$23.50	$23.50
Purchase #7	$218.54	3.629%	$226.4708	$226.47	$226.45	$226.50
7 purchase totals =	$1,046.22		$1,131.4385	$1,131.43	$1,131.40	$1,131.40