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	$25.50	9.409%	$27.8993	$27.90	$27.90	$27.90
Purchase #2	$109.77	3.703%	$113.8348	$113.83	$113.85	$113.80
Purchase #3	$228.32	11.611%	$254.8302	$254.83	$254.85	$254.80
Purchase #4	$225.63	9.387%	$246.8099	$246.81	$246.80	$246.80
Purchase #5	$210.38	13.233%	$238.2196	$238.22	$238.20	$238.20
Purchase #6	$189.60	4.869%	$198.8316	$198.83	$198.85	$198.80
Purchase #7	$116.29	3.201%	$120.0124	$120.01	$120.00	$120.00
7 purchase totals =	$1,105.49		$1,200.4378	$1,200.43	$1,200.45	$1,200.30