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	$128.36	3.512%	$132.868	$132.87	$132.85	$132.90
Purchase #2	$134.27	6.371%	$142.8243	$142.82	$142.80	$142.80
Purchase #3	$161.45	7.656%	$173.8106	$173.81	$173.80	$173.80
Purchase #4	$242.78	5.257%	$255.5429	$255.54	$255.55	$255.50
Purchase #5	$61.66	4.372%	$64.3558	$64.36	$64.35	$64.40
Purchase #6	$40.38	6.536%	$43.0192	$43.02	$43.00	$43.00
Purchase #7	$19.86	4.582%	$20.77	$20.77	$20.75	$20.80
7 purchase totals =	$788.76		$833.1908	$833.19	$833.10	$833.20