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	$88.70	12.751%	$100.0101	$100.01	$100.00	$100.00
Purchase #2	$228.98	11.840%	$256.0912	$256.09	$256.10	$256.10
Purchase #3	$105.80	10.861%	$117.2909	$117.29	$117.30	$117.30
Purchase #4	$165.97	9.844%	$182.3081	$182.31	$182.30	$182.30
Purchase #5	$192.57	3.340%	$199.0018	$199.00	$199.00	$199.00
Purchase #6	$190.82	4.831%	$200.0385	$200.04	$200.05	$200.00
Purchase #7	$119.52	3.241%	$123.3936	$123.39	$123.40	$123.40
7 purchase totals =	$1,092.36		$1,178.1342	$1,178.13	$1,178.15	$1,178.10