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	$228.53	13.549%	$259.4935	$259.49	$259.50	$259.50
Purchase #2	$66.68	7.118%	$71.4263	$71.43	$71.45	$71.40
Purchase #3	$208.27	13.622%	$236.6405	$236.64	$236.65	$236.60
Purchase #4	$192.43	13.749%	$218.8872	$218.89	$218.90	$218.90
Purchase #5	$120.77	7.675%	$130.0391	$130.04	$130.05	$130.00
Purchase #6	$35.67	13.823%	$40.6007	$40.60	$40.60	$40.60
Purchase #7	$247.72	9.357%	$270.8992	$270.90	$270.90	$270.90
7 purchase totals =	$1,100.07		$1,227.9865	$1,227.99	$1,228.05	$1,227.90