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	$131.47	10.697%	$145.5333	$145.53	$145.55	$145.50
Purchase #2	$246.88	13.390%	$279.9372	$279.94	$279.95	$279.90
Purchase #3	$38.92	11.788%	$43.5079	$43.51	$43.50	$43.50
Purchase #4	$45.88	12.504%	$51.6168	$51.62	$51.60	$51.60
Purchase #5	$197.83	13.234%	$224.0108	$224.01	$224.00	$224.00
Purchase #6	$111.50	12.756%	$125.7229	$125.72	$125.70	$125.70
Purchase #7	$125.46	8.418%	$136.0212	$136.02	$136.00	$136.00
7 purchase totals =	$897.94		$1,006.3501	$1,006.35	$1,006.30	$1,006.20