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	$226.58	9.239%	$247.5137	$247.51	$247.50	$247.50
Purchase #2	$93.90	8.660%	$102.0317	$102.03	$102.05	$102.00
Purchase #3	$138.84	4.770%	$145.4627	$145.46	$145.45	$145.50
Purchase #4	$56.42	11.484%	$62.8993	$62.90	$62.90	$62.90
Purchase #5	$202.99	3.868%	$210.8417	$210.84	$210.85	$210.80
Purchase #6	$172.79	10.520%	$190.9675	$190.97	$190.95	$191.00
Purchase #7	$180.69	5.645%	$190.89	$190.89	$190.90	$190.90
7 purchase totals =	$1,072.21		$1,150.6066	$1,150.60	$1,150.60	$1,150.60