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	$37.32	3.124%	$38.4859	$38.49	$38.50	$38.50
Purchase #2	$127.47	13.234%	$144.3394	$144.34	$144.35	$144.30
Purchase #3	$209.61	11.412%	$233.5307	$233.53	$233.55	$233.50
Purchase #4	$199.75	5.379%	$210.4946	$210.49	$210.50	$210.50
Purchase #5	$136.44	4.784%	$142.9673	$142.97	$142.95	$143.00
Purchase #6	$61.58	3.516%	$63.7452	$63.75	$63.75	$63.70
Purchase #7	$231.65	10.365%	$255.6605	$255.66	$255.65	$255.70
7 purchase totals =	$1,003.82		$1,089.2236	$1,089.23	$1,089.25	$1,089.20