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	$100.74	4.726%	$105.501	$105.50	$105.50	$105.50
Purchase #2	$136.66	3.124%	$140.9293	$140.93	$140.95	$140.90
Purchase #3	$97.25	5.292%	$102.3965	$102.40	$102.40	$102.40
Purchase #4	$80.30	8.448%	$87.0837	$87.08	$87.10	$87.10
Purchase #5	$10.56	6.329%	$11.2283	$11.23	$11.25	$11.20
Purchase #6	$77.92	5.780%	$82.4238	$82.42	$82.40	$82.40
Purchase #7	$18.82	10.710%	$20.8356	$20.84	$20.85	$20.80
7 purchase totals =	$522.25		$550.3982	$550.40	$550.45	$550.30