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	$136.56	4.124%	$142.1917	$142.19	$142.20	$142.20
Purchase #2	$80.80	11.402%	$90.0128	$90.01	$90.00	$90.00
Purchase #3	$40.96	5.866%	$43.3627	$43.36	$43.35	$43.40
Purchase #4	$207.39	11.535%	$231.3124	$231.31	$231.30	$231.30
Purchase #5	$6.61	3.703%	$6.8548	$6.85	$6.85	$6.90
Purchase #6	$198.40	8.582%	$215.4267	$215.43	$215.45	$215.40
Purchase #7	$207.60	7.667%	$223.5167	$223.52	$223.50	$223.50
7 purchase totals =	$878.32		$952.6778	$952.67	$952.65	$952.70