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	$181.95	6.529%	$193.8295	$193.83	$193.85	$193.80
Purchase #2	$128.87	10.243%	$142.0702	$142.07	$142.05	$142.10
Purchase #3	$172.95	6.443%	$184.0932	$184.09	$184.10	$184.10
Purchase #4	$33.67	13.300%	$38.1481	$38.15	$38.15	$38.10
Purchase #5	$14.80	7.147%	$15.8578	$15.86	$15.85	$15.90
Purchase #6	$161.83	7.173%	$173.4381	$173.44	$173.45	$173.40
Purchase #7	$214.63	7.859%	$231.4978	$231.50	$231.50	$231.50
7 purchase totals =	$908.70		$978.9347	$978.94	$978.95	$978.90