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	$142.40	8.336%	$154.2705	$154.27	$154.25	$154.30
Purchase #2	$128.52	8.172%	$139.0227	$139.02	$139.00	$139.00
Purchase #3	$166.73	11.770%	$186.3541	$186.35	$186.35	$186.40
Purchase #4	$153.87	12.365%	$172.896	$172.90	$172.90	$172.90
Purchase #5	$95.34	5.225%	$100.3215	$100.32	$100.30	$100.30
Purchase #6	$43.62	3.261%	$45.0424	$45.04	$45.05	$45.00
Purchase #7	$38.94	7.393%	$41.8188	$41.82	$41.80	$41.80
7 purchase totals =	$769.42		$839.7260	$839.72	$839.65	$839.70