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	$199.27	4.462%	$208.1614	$208.16	$208.15	$208.20
Purchase #2	$213.85	11.837%	$239.1634	$239.16	$239.15	$239.20
Purchase #3	$67.47	7.409%	$72.4689	$72.47	$72.45	$72.50
Purchase #4	$179.41	9.614%	$196.6585	$196.66	$196.65	$196.70
Purchase #5	$38.98	4.636%	$40.7871	$40.79	$40.80	$40.80
Purchase #6	$85.81	12.747%	$96.7482	$96.75	$96.75	$96.70
Purchase #7	$102.95	12.682%	$116.0061	$116.01	$116.00	$116.00
7 purchase totals =	$887.74		$969.9936	$970.00	$969.95	$970.10