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	$243.36	6.364%	$258.8474	$258.85	$258.85	$258.80
Purchase #2	$205.32	5.788%	$217.2039	$217.20	$217.20	$217.20
Purchase #3	$35.66	13.847%	$40.5978	$40.60	$40.60	$40.60
Purchase #4	$138.90	3.870%	$144.2754	$144.28	$144.30	$144.30
Purchase #5	$73.49	12.814%	$82.907	$82.91	$82.90	$82.90
Purchase #6	$81.47	6.438%	$86.715	$86.72	$86.70	$86.70
Purchase #7	$111.27	4.526%	$116.3061	$116.31	$116.30	$116.30
7 purchase totals =	$889.47		$946.8526	$946.87	$946.85	$946.80