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	$136.73	13.225%	$154.8125	$154.81	$154.80	$154.80
Purchase #2	$86.97	6.778%	$92.8648	$92.86	$92.85	$92.90
Purchase #3	$27.27	11.659%	$30.4494	$30.45	$30.45	$30.40
Purchase #4	$77.54	6.834%	$82.8391	$82.84	$82.85	$82.80
Purchase #5	$43.98	13.158%	$49.7669	$49.77	$49.75	$49.80
Purchase #6	$8.98	12.212%	$10.0766	$10.08	$10.10	$10.10
Purchase #7	$118.77	10.789%	$131.5841	$131.58	$131.60	$131.60
7 purchase totals =	$500.24		$552.3934	$552.39	$552.40	$552.40