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	$16.47	5.608%	$17.3936	$17.39	$17.40	$17.40
Purchase #2	$156.74	4.709%	$164.1209	$164.12	$164.10	$164.10
Purchase #3	$154.78	6.493%	$164.8299	$164.83	$164.85	$164.80
Purchase #4	$13.41	13.714%	$15.249	$15.25	$15.25	$15.20
Purchase #5	$72.34	3.141%	$74.6122	$74.61	$74.60	$74.60
Purchase #6	$56.42	10.436%	$62.308	$62.31	$62.30	$62.30
Purchase #7	$246.47	11.617%	$275.1024	$275.10	$275.10	$275.10
7 purchase totals =	$716.63		$773.6160	$773.61	$773.60	$773.50