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	$243.28	12.554%	$273.8214	$273.82	$273.80	$273.80
Purchase #2	$31.54	8.741%	$34.2969	$34.30	$34.30	$34.30
Purchase #3	$143.49	4.716%	$150.257	$150.26	$150.25	$150.30
Purchase #4	$121.41	8.288%	$131.4725	$131.47	$131.45	$131.50
Purchase #5	$90.85	5.546%	$95.8885	$95.89	$95.90	$95.90
Purchase #6	$48.88	7.738%	$52.6623	$52.66	$52.65	$52.70
Purchase #7	$84.42	3.564%	$87.4287	$87.43	$87.45	$87.40
7 purchase totals =	$763.87		$825.8273	$825.83	$825.80	$825.90