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	$20.58	11.279%	$22.9012	$22.90	$22.90	$22.90
Purchase #2	$123.40	6.788%	$131.7764	$131.78	$131.80	$131.80
Purchase #3	$69.96	3.155%	$72.1672	$72.17	$72.15	$72.20
Purchase #4	$80.64	12.504%	$90.7232	$90.72	$90.70	$90.70
Purchase #5	$154.35	4.665%	$161.5504	$161.55	$161.55	$161.60
Purchase #6	$160.66	10.219%	$177.0778	$177.08	$177.10	$177.10
Purchase #7	$49.48	3.259%	$51.0926	$51.09	$51.10	$51.10
7 purchase totals =	$659.07		$707.2888	$707.29	$707.30	$707.40