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	$79.85	7.234%	$85.6263	$85.63	$85.65	$85.60
Purchase #2	$87.64	7.129%	$93.8879	$93.89	$93.90	$93.90
Purchase #3	$43.88	4.284%	$45.7598	$45.76	$45.75	$45.80
Purchase #4	$120.61	11.534%	$134.5212	$134.52	$134.50	$134.50
Purchase #5	$121.25	8.567%	$131.6375	$131.64	$131.65	$131.60
Purchase #6	$51.71	8.202%	$55.9513	$55.95	$55.95	$56.00
Purchase #7	$104.80	10.164%	$115.4519	$115.45	$115.45	$115.50
7 purchase totals =	$609.74		$662.8359	$662.84	$662.85	$662.90