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	$112.78	9.544%	$123.5437	$123.54	$123.55	$123.50
Purchase #2	$230.40	7.841%	$248.4657	$248.47	$248.45	$248.50
Purchase #3	$213.37	12.626%	$240.3101	$240.31	$240.30	$240.30
Purchase #4	$204.43	11.381%	$227.6962	$227.70	$227.70	$227.70
Purchase #5	$71.87	13.497%	$81.5703	$81.57	$81.55	$81.60
Purchase #6	$172.94	13.832%	$196.8611	$196.86	$196.85	$196.90
Purchase #7	$194.50	10.830%	$215.5644	$215.56	$215.55	$215.60
7 purchase totals =	$1,200.29		$1,334.0115	$1,334.01	$1,333.95	$1,334.10