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	$29.51	5.377%	$31.0968	$31.10	$31.10	$31.10
Purchase #2	$111.43	10.440%	$123.0633	$123.06	$123.05	$123.10
Purchase #3	$37.78	13.418%	$42.8493	$42.85	$42.85	$42.80
Purchase #4	$183.59	4.392%	$191.6533	$191.65	$191.65	$191.70
Purchase #5	$191.35	8.357%	$207.3411	$207.34	$207.35	$207.30
Purchase #6	$112.38	6.630%	$119.8308	$119.83	$119.85	$119.80
Purchase #7	$90.75	13.322%	$102.8397	$102.84	$102.85	$102.80
7 purchase totals =	$756.79		$818.6743	$818.67	$818.70	$818.60