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	$38.86	3.556%	$40.2419	$40.24	$40.25	$40.20
Purchase #2	$229.55	13.628%	$260.8331	$260.83	$260.85	$260.80
Purchase #3	$212.28	7.165%	$227.4899	$227.49	$227.50	$227.50
Purchase #4	$82.92	9.606%	$90.8853	$90.89	$90.90	$90.90
Purchase #5	$23.29	6.423%	$24.7859	$24.79	$24.80	$24.80
Purchase #6	$55.99	10.387%	$61.8057	$61.81	$61.80	$61.80
Purchase #7	$150.35	13.290%	$170.3315	$170.33	$170.35	$170.30
7 purchase totals =	$793.24		$876.3733	$876.38	$876.45	$876.30