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	$241.78	6.861%	$258.3685	$258.37	$258.35	$258.40
Purchase #2	$71.98	9.497%	$78.8159	$78.82	$78.80	$78.80
Purchase #3	$204.31	13.536%	$231.9654	$231.97	$231.95	$232.00
Purchase #4	$131.32	8.800%	$142.8762	$142.88	$142.90	$142.90
Purchase #5	$177.58	4.456%	$185.493	$185.49	$185.50	$185.50
Purchase #6	$108.35	4.433%	$113.1532	$113.15	$113.15	$113.20
Purchase #7	$247.69	13.187%	$280.3529	$280.35	$280.35	$280.40
7 purchase totals =	$1,183.01		$1,291.0251	$1,291.03	$1,291.00	$1,291.20