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	$78.77	5.766%	$83.3119	$83.31	$83.30	$83.30
Purchase #2	$230.60	12.737%	$259.9715	$259.97	$259.95	$260.00
Purchase #3	$113.56	12.580%	$127.8458	$127.85	$127.85	$127.80
Purchase #4	$213.85	13.127%	$241.9221	$241.92	$241.90	$241.90
Purchase #5	$68.89	9.392%	$75.3601	$75.36	$75.35	$75.40
Purchase #6	$206.95	6.654%	$220.7205	$220.72	$220.70	$220.70
Purchase #7	$35.70	13.492%	$40.5166	$40.52	$40.50	$40.50
7 purchase totals =	$948.32		$1,049.6485	$1,049.65	$1,049.55	$1,049.60