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	$140.46	7.117%	$150.4565	$150.46	$150.45	$150.50
Purchase #2	$25.90	8.153%	$28.0116	$28.01	$28.00	$28.00
Purchase #3	$200.83	6.225%	$213.3317	$213.33	$213.35	$213.30
Purchase #4	$141.79	9.681%	$155.5167	$155.52	$155.50	$155.50
Purchase #5	$144.83	13.410%	$164.2517	$164.25	$164.25	$164.30
Purchase #6	$76.42	7.509%	$82.1584	$82.16	$82.15	$82.20
Purchase #7	$61.26	13.850%	$69.7445	$69.74	$69.75	$69.70
7 purchase totals =	$791.49		$863.4711	$863.47	$863.45	$863.50