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	$223.59	10.778%	$247.6885	$247.69	$247.70	$247.70
Purchase #2	$238.54	7.409%	$256.2134	$256.21	$256.20	$256.20
Purchase #3	$156.78	6.724%	$167.3219	$167.32	$167.30	$167.30
Purchase #4	$109.94	13.352%	$124.6192	$124.62	$124.60	$124.60
Purchase #5	$92.49	8.452%	$100.3073	$100.31	$100.30	$100.30
Purchase #6	$215.99	11.757%	$241.3839	$241.38	$241.40	$241.40
Purchase #7	$130.51	9.199%	$142.5156	$142.52	$142.50	$142.50
7 purchase totals =	$1,167.84		$1,280.0498	$1,280.05	$1,280.00	$1,280.00