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	$70.42	10.430%	$77.7648	$77.76	$77.75	$77.80
Purchase #2	$154.76	7.435%	$166.2664	$166.27	$166.25	$166.30
Purchase #3	$152.52	10.184%	$168.0526	$168.05	$168.05	$168.10
Purchase #4	$34.87	10.323%	$38.4696	$38.47	$38.45	$38.50
Purchase #5	$39.98	8.766%	$43.4846	$43.48	$43.50	$43.50
Purchase #6	$50.32	5.201%	$52.9371	$52.94	$52.95	$52.90
Purchase #7	$17.94	8.620%	$19.4864	$19.49	$19.50	$19.50
7 purchase totals =	$520.81		$566.4615	$566.46	$566.45	$566.60