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	$135.50	12.528%	$152.4754	$152.48	$152.50	$152.50
Purchase #2	$205.57	5.564%	$217.0079	$217.01	$217.00	$217.00
Purchase #3	$103.98	5.180%	$109.3662	$109.37	$109.35	$109.40
Purchase #4	$133.90	5.509%	$141.2766	$141.28	$141.30	$141.30
Purchase #5	$36.29	5.337%	$38.2268	$38.23	$38.25	$38.20
Purchase #6	$243.42	4.456%	$254.2668	$254.27	$254.25	$254.30
Purchase #7	$97.40	8.265%	$105.4501	$105.45	$105.45	$105.50
7 purchase totals =	$956.06		$1,018.0698	$1,018.09	$1,018.10	$1,018.20