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	$227.98	12.201%	$255.7958	$255.80	$255.80	$255.80
Purchase #2	$143.25	10.129%	$157.7598	$157.76	$157.75	$157.80
Purchase #3	$114.98	9.555%	$125.9663	$125.97	$125.95	$126.00
Purchase #4	$72.86	7.711%	$78.4782	$78.48	$78.50	$78.50
Purchase #5	$223.47	6.737%	$238.5252	$238.53	$238.55	$238.50
Purchase #6	$91.48	13.548%	$103.8737	$103.87	$103.85	$103.90
Purchase #7	$31.93	12.554%	$35.9385	$35.94	$35.95	$35.90
7 purchase totals =	$905.95		$996.3375	$996.35	$996.35	$996.40