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	$55.51	4.294%	$57.8936	$57.89	$57.90	$57.90
Purchase #2	$172.89	11.418%	$192.6306	$192.63	$192.65	$192.60
Purchase #3	$132.87	7.284%	$142.5483	$142.55	$142.55	$142.50
Purchase #4	$222.65	13.175%	$251.9841	$251.98	$252.00	$252.00
Purchase #5	$28.96	13.173%	$32.7749	$32.77	$32.75	$32.80
Purchase #6	$224.78	13.726%	$255.6333	$255.63	$255.65	$255.60
Purchase #7	$65.94	11.278%	$73.3767	$73.38	$73.40	$73.40
7 purchase totals =	$903.60		$1,006.8415	$1,006.83	$1,006.90	$1,006.80