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	$217.61	7.309%	$233.5151	$233.52	$233.50	$233.50
Purchase #2	$66.98	11.729%	$74.8361	$74.84	$74.85	$74.80
Purchase #3	$60.32	11.765%	$67.4166	$67.42	$67.40	$67.40
Purchase #4	$123.67	10.692%	$136.8928	$136.89	$136.90	$136.90
Purchase #5	$222.82	8.559%	$241.8912	$241.89	$241.90	$241.90
Purchase #6	$204.47	5.597%	$215.9142	$215.91	$215.90	$215.90
Purchase #7	$93.62	7.294%	$100.4486	$100.45	$100.45	$100.40
7 purchase totals =	$989.49		$1,070.9146	$1,070.92	$1,070.90	$1,070.80