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	$39.59	8.141%	$42.813	$42.81	$42.80	$42.80
Purchase #2	$14.60	8.262%	$15.8063	$15.81	$15.80	$15.80
Purchase #3	$132.71	7.588%	$142.78	$142.78	$142.80	$142.80
Purchase #4	$63.94	9.834%	$70.2279	$70.23	$70.25	$70.20
Purchase #5	$154.80	4.293%	$161.4456	$161.45	$161.45	$161.40
Purchase #6	$74.85	13.570%	$85.0071	$85.01	$85.00	$85.00
Purchase #7	$213.32	4.626%	$223.1882	$223.19	$223.20	$223.20
7 purchase totals =	$693.81		$741.2681	$741.28	$741.30	$741.20