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	$245.32	13.339%	$278.0432	$278.04	$278.05	$278.00
Purchase #2	$199.35	9.205%	$217.7002	$217.70	$217.70	$217.70
Purchase #3	$176.39	7.304%	$189.2735	$189.27	$189.25	$189.30
Purchase #4	$96.59	6.573%	$102.9389	$102.94	$102.95	$102.90
Purchase #5	$163.29	3.363%	$168.7814	$168.78	$168.80	$168.80
Purchase #6	$84.92	6.568%	$90.4975	$90.50	$90.50	$90.50
Purchase #7	$111.85	6.723%	$119.3697	$119.37	$119.35	$119.40
7 purchase totals =	$1,077.71		$1,166.6044	$1,166.60	$1,166.60	$1,166.60