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	$22.58	6.719%	$24.0972	$24.10	$24.10	$24.10
Purchase #2	$191.80	12.377%	$215.5391	$215.54	$215.55	$215.50
Purchase #3	$221.92	3.145%	$228.8994	$228.90	$228.90	$228.90
Purchase #4	$37.38	9.239%	$40.8335	$40.83	$40.85	$40.80
Purchase #5	$136.35	8.736%	$148.2615	$148.26	$148.25	$148.30
Purchase #6	$70.38	10.314%	$77.639	$77.64	$77.65	$77.60
Purchase #7	$137.48	5.348%	$144.8324	$144.83	$144.85	$144.80
7 purchase totals =	$817.89		$880.1021	$880.10	$880.15	$880.00