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	$179.37	3.559%	$185.7538	$185.75	$185.75	$185.80
Purchase #2	$26.55	4.741%	$27.8087	$27.81	$27.80	$27.80
Purchase #3	$37.87	8.605%	$41.1287	$41.13	$41.15	$41.10
Purchase #4	$93.57	7.366%	$100.4624	$100.46	$100.45	$100.50
Purchase #5	$124.86	3.294%	$128.9729	$128.97	$128.95	$129.00
Purchase #6	$20.47	5.857%	$21.6689	$21.67	$21.65	$21.70
Purchase #7	$68.35	5.777%	$72.2986	$72.30	$72.30	$72.30
7 purchase totals =	$551.04		$578.0940	$578.09	$578.05	$578.20