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	$31.70	4.280%	$33.0568	$33.06	$33.05	$33.10
Purchase #2	$102.52	4.259%	$106.8863	$106.89	$106.90	$106.90
Purchase #3	$28.85	9.509%	$31.5933	$31.59	$31.60	$31.60
Purchase #4	$211.67	3.115%	$218.2635	$218.26	$218.25	$218.30
Purchase #5	$220.75	6.330%	$234.7235	$234.72	$234.70	$234.70
Purchase #6	$218.80	10.475%	$241.7193	$241.72	$241.70	$241.70
Purchase #7	$126.88	3.633%	$131.4896	$131.49	$131.50	$131.50
7 purchase totals =	$941.17		$997.7323	$997.73	$997.70	$997.80