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	$247.36	3.521%	$256.0695	$256.07	$256.05	$256.10
Purchase #2	$232.65	10.561%	$257.2202	$257.22	$257.20	$257.20
Purchase #3	$39.42	11.317%	$43.8812	$43.88	$43.90	$43.90
Purchase #4	$34.98	13.455%	$39.6866	$39.69	$39.70	$39.70
Purchase #5	$82.66	9.211%	$90.2738	$90.27	$90.25	$90.30
Purchase #6	$16.72	4.768%	$17.5172	$17.52	$17.50	$17.50
Purchase #7	$171.60	7.550%	$184.5558	$184.56	$184.55	$184.60
7 purchase totals =	$825.39		$889.2043	$889.21	$889.15	$889.30