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	$246.58	3.536%	$255.2991	$255.30	$255.30	$255.30
Purchase #2	$28.29	11.494%	$31.5417	$31.54	$31.55	$31.50
Purchase #3	$235.67	10.549%	$260.5308	$260.53	$260.55	$260.50
Purchase #4	$168.41	9.495%	$184.4005	$184.40	$184.40	$184.40
Purchase #5	$17.32	12.195%	$19.4322	$19.43	$19.45	$19.40
Purchase #6	$73.60	6.565%	$78.4318	$78.43	$78.45	$78.40
Purchase #7	$248.81	8.435%	$269.7971	$269.80	$269.80	$269.80
7 purchase totals =	$1,018.68		$1,099.4332	$1,099.43	$1,099.50	$1,099.30