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	$107.46	8.784%	$116.8993	$116.90	$116.90	$116.90
Purchase #2	$144.85	13.555%	$164.4844	$164.48	$164.50	$164.50
Purchase #3	$62.54	12.464%	$70.335	$70.34	$70.35	$70.30
Purchase #4	$32.43	10.659%	$35.8867	$35.89	$35.90	$35.90
Purchase #5	$234.71	3.403%	$242.6972	$242.70	$242.70	$242.70
Purchase #6	$121.93	7.871%	$131.5271	$131.53	$131.55	$131.50
Purchase #7	$225.92	5.849%	$239.1341	$239.13	$239.15	$239.10
7 purchase totals =	$929.84		$1,000.9638	$1,000.97	$1,001.05	$1,000.90