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	$213.84	4.373%	$223.1912	$223.19	$223.20	$223.20
Purchase #2	$84.85	5.409%	$89.4395	$89.44	$89.45	$89.40
Purchase #3	$106.96	6.814%	$114.2483	$114.25	$114.25	$114.20
Purchase #4	$38.79	3.814%	$40.2695	$40.27	$40.25	$40.30
Purchase #5	$190.45	4.215%	$198.4775	$198.48	$198.50	$198.50
Purchase #6	$223.31	10.420%	$246.5789	$246.58	$246.60	$246.60
Purchase #7	$242.70	11.486%	$270.5765	$270.58	$270.60	$270.60
7 purchase totals =	$1,100.90		$1,182.7814	$1,182.79	$1,182.85	$1,182.80