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	$95.73	5.338%	$100.8401	$100.84	$100.85	$100.80
Purchase #2	$16.89	8.181%	$18.2718	$18.27	$18.25	$18.30
Purchase #3	$82.93	5.853%	$87.7839	$87.78	$87.80	$87.80
Purchase #4	$142.47	9.874%	$156.5375	$156.54	$156.55	$156.50
Purchase #5	$93.73	9.778%	$102.8949	$102.89	$102.90	$102.90
Purchase #6	$59.43	5.155%	$62.4936	$62.49	$62.50	$62.50
Purchase #7	$44.50	11.107%	$49.4426	$49.44	$49.45	$49.40
7 purchase totals =	$535.68		$578.2644	$578.25	$578.30	$578.20