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	$152.43	4.183%	$158.8061	$158.81	$158.80	$158.80
Purchase #2	$147.58	13.196%	$167.0547	$167.05	$167.05	$167.10
Purchase #3	$229.99	4.467%	$240.2637	$240.26	$240.25	$240.30
Purchase #4	$108.61	13.641%	$123.4255	$123.43	$123.45	$123.40
Purchase #5	$17.47	10.719%	$19.3426	$19.34	$19.35	$19.30
Purchase #6	$140.58	6.745%	$150.0621	$150.06	$150.05	$150.10
Purchase #7	$19.42	8.466%	$21.0641	$21.06	$21.05	$21.10
7 purchase totals =	$816.08		$880.0188	$880.01	$880.00	$880.10