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	$236.88	12.696%	$266.9543	$266.95	$266.95	$267.00
Purchase #2	$78.25	13.228%	$88.6009	$88.60	$88.60	$88.60
Purchase #3	$31.84	11.385%	$35.465	$35.47	$35.45	$35.50
Purchase #4	$84.61	5.686%	$89.4209	$89.42	$89.40	$89.40
Purchase #5	$107.57	5.509%	$113.496	$113.50	$113.50	$113.50
Purchase #6	$73.45	12.546%	$82.665	$82.67	$82.65	$82.70
Purchase #7	$36.51	13.461%	$41.4246	$41.42	$41.40	$41.40
7 purchase totals =	$649.11		$718.0267	$718.03	$717.95	$718.10