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	$85.38	11.621%	$95.302	$95.30	$95.30	$95.30
Purchase #2	$196.26	13.239%	$222.2429	$222.24	$222.25	$222.20
Purchase #3	$111.69	8.789%	$121.5064	$121.51	$121.50	$121.50
Purchase #4	$34.60	11.723%	$38.6562	$38.66	$38.65	$38.70
Purchase #5	$77.82	13.662%	$88.4518	$88.45	$88.45	$88.50
Purchase #6	$97.64	12.254%	$109.6048	$109.60	$109.60	$109.60
Purchase #7	$138.93	11.207%	$154.4999	$154.50	$154.50	$154.50
7 purchase totals =	$742.32		$830.2640	$830.26	$830.25	$830.30