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	$22.94	11.127%	$25.4925	$25.49	$25.50	$25.50
Purchase #2	$132.42	6.779%	$141.3968	$141.40	$141.40	$141.40
Purchase #3	$226.65	13.260%	$256.7038	$256.70	$256.70	$256.70
Purchase #4	$198.64	10.795%	$220.0832	$220.08	$220.10	$220.10
Purchase #5	$242.44	7.192%	$259.8763	$259.88	$259.90	$259.90
Purchase #6	$81.93	10.337%	$90.3991	$90.40	$90.40	$90.40
Purchase #7	$22.80	11.870%	$25.5064	$25.51	$25.50	$25.50
7 purchase totals =	$927.82		$1,019.4581	$1,019.46	$1,019.50	$1,019.50