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	$20.92	4.332%	$21.8263	$21.83	$21.85	$21.80
Purchase #2	$92.44	8.487%	$100.2854	$100.29	$100.30	$100.30
Purchase #3	$181.52	10.402%	$200.4017	$200.40	$200.40	$200.40
Purchase #4	$36.38	10.734%	$40.285	$40.29	$40.30	$40.30
Purchase #5	$211.40	13.197%	$239.2985	$239.30	$239.30	$239.30
Purchase #6	$90.86	11.642%	$101.4379	$101.44	$101.45	$101.40
Purchase #7	$66.51	10.700%	$73.6266	$73.63	$73.65	$73.60
7 purchase totals =	$700.03		$777.1614	$777.18	$777.25	$777.10