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	$122.80	3.196%	$126.7247	$126.72	$126.70	$126.70
Purchase #2	$193.38	5.241%	$203.515	$203.52	$203.50	$203.50
Purchase #3	$16.61	13.314%	$18.8215	$18.82	$18.80	$18.80
Purchase #4	$123.96	3.680%	$128.5217	$128.52	$128.50	$128.50
Purchase #5	$222.29	11.838%	$248.6047	$248.60	$248.60	$248.60
Purchase #6	$20.77	3.536%	$21.5044	$21.50	$21.50	$21.50
Purchase #7	$10.88	10.329%	$12.0038	$12.00	$12.00	$12.00
7 purchase totals =	$710.69		$759.6958	$759.68	$759.60	$759.60