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	$72.66	13.640%	$82.5708	$82.57	$82.55	$82.60
Purchase #2	$185.81	11.152%	$206.5315	$206.53	$206.55	$206.50
Purchase #3	$175.49	6.712%	$187.2689	$187.27	$187.25	$187.30
Purchase #4	$18.47	9.492%	$20.2232	$20.22	$20.20	$20.20
Purchase #5	$198.50	7.479%	$213.3458	$213.35	$213.35	$213.30
Purchase #6	$244.25	9.243%	$266.826	$266.83	$266.85	$266.80
Purchase #7	$120.92	12.789%	$136.3845	$136.38	$136.40	$136.40
7 purchase totals =	$1,016.10		$1,113.1507	$1,113.15	$1,113.15	$1,113.10