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	$72.79	5.652%	$76.9041	$76.90	$76.90	$76.90
Purchase #2	$58.71	8.181%	$63.5131	$63.51	$63.50	$63.50
Purchase #3	$50.45	3.649%	$52.2909	$52.29	$52.30	$52.30
Purchase #4	$28.85	7.630%	$31.0513	$31.05	$31.05	$31.10
Purchase #5	$80.45	10.796%	$89.1354	$89.14	$89.15	$89.10
Purchase #6	$33.38	6.655%	$35.6014	$35.60	$35.60	$35.60
Purchase #7	$148.89	4.757%	$155.9727	$155.97	$155.95	$156.00
7 purchase totals =	$473.52		$504.4689	$504.46	$504.45	$504.50