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	$11.87	13.697%	$13.4958	$13.50	$13.50	$13.50
Purchase #2	$133.86	3.359%	$138.3564	$138.36	$138.35	$138.40
Purchase #3	$106.93	10.222%	$117.8604	$117.86	$117.85	$117.90
Purchase #4	$134.98	11.177%	$150.0667	$150.07	$150.05	$150.10
Purchase #5	$68.44	11.564%	$76.3544	$76.35	$76.35	$76.40
Purchase #6	$175.59	12.107%	$196.8487	$196.85	$196.85	$196.80
Purchase #7	$94.54	9.427%	$103.4523	$103.45	$103.45	$103.50
7 purchase totals =	$726.21		$796.4347	$796.44	$796.40	$796.60