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	$132.52	5.151%	$139.3461	$139.35	$139.35	$139.30
Purchase #2	$157.75	6.840%	$168.5401	$168.54	$168.55	$168.50
Purchase #3	$209.46	12.299%	$235.2215	$235.22	$235.20	$235.20
Purchase #4	$159.60	5.410%	$168.2344	$168.23	$168.25	$168.20
Purchase #5	$84.45	6.341%	$89.805	$89.81	$89.80	$89.80
Purchase #6	$195.58	9.306%	$213.7807	$213.78	$213.80	$213.80
Purchase #7	$209.82	7.636%	$225.8419	$225.84	$225.85	$225.80
7 purchase totals =	$1,149.18		$1,240.7697	$1,240.77	$1,240.80	$1,240.60