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	$6.80	12.473%	$7.6482	$7.65	$7.65	$7.60
Purchase #2	$178.98	11.177%	$198.9846	$198.98	$199.00	$199.00
Purchase #3	$186.52	10.385%	$205.8901	$205.89	$205.90	$205.90
Purchase #4	$181.42	10.709%	$200.8483	$200.85	$200.85	$200.80
Purchase #5	$11.52	6.194%	$12.2335	$12.23	$12.25	$12.20
Purchase #6	$220.62	10.159%	$243.0328	$243.03	$243.05	$243.00
Purchase #7	$77.96	5.786%	$82.4708	$82.47	$82.45	$82.50
7 purchase totals =	$863.82		$951.1083	$951.10	$951.15	$951.00