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	$126.88	9.540%	$138.9844	$138.98	$139.00	$139.00
Purchase #2	$117.65	13.519%	$133.5551	$133.56	$133.55	$133.60
Purchase #3	$13.78	9.578%	$15.0998	$15.10	$15.10	$15.10
Purchase #4	$77.52	6.849%	$82.8293	$82.83	$82.85	$82.80
Purchase #5	$115.89	10.193%	$127.7027	$127.70	$127.70	$127.70
Purchase #6	$126.54	8.616%	$137.4427	$137.44	$137.45	$137.40
Purchase #7	$18.83	6.736%	$20.0984	$20.10	$20.10	$20.10
7 purchase totals =	$597.09		$655.7124	$655.71	$655.75	$655.70