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	$212.80	12.258%	$238.885	$238.89	$238.90	$238.90
Purchase #2	$83.35	8.664%	$90.5714	$90.57	$90.55	$90.60
Purchase #3	$250.47	6.203%	$266.0067	$266.01	$266.00	$266.00
Purchase #4	$87.82	5.180%	$92.3691	$92.37	$92.35	$92.40
Purchase #5	$95.26	10.782%	$105.5309	$105.53	$105.55	$105.50
Purchase #6	$206.25	10.414%	$227.7289	$227.73	$227.75	$227.70
Purchase #7	$61.89	5.559%	$65.3305	$65.33	$65.35	$65.30
7 purchase totals =	$997.84		$1,086.4225	$1,086.43	$1,086.45	$1,086.40