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	$6.42	7.554%	$6.905	$6.91	$6.90	$6.90
Purchase #2	$16.79	11.860%	$18.7813	$18.78	$18.80	$18.80
Purchase #3	$49.35	7.330%	$52.9674	$52.97	$52.95	$53.00
Purchase #4	$243.73	8.548%	$264.564	$264.56	$264.55	$264.60
Purchase #5	$138.83	4.338%	$144.8524	$144.85	$144.85	$144.90
Purchase #6	$90.97	13.838%	$103.5584	$103.56	$103.55	$103.60
Purchase #7	$103.78	13.182%	$117.4603	$117.46	$117.45	$117.50
7 purchase totals =	$649.87		$709.0888	$709.09	$709.05	$709.30