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	$129.89	5.651%	$137.2301	$137.23	$137.25	$137.20
Purchase #2	$221.83	7.566%	$238.6137	$238.61	$238.60	$238.60
Purchase #3	$7.97	4.525%	$8.3306	$8.33	$8.35	$8.30
Purchase #4	$217.37	9.763%	$238.5918	$238.59	$238.60	$238.60
Purchase #5	$38.90	10.739%	$43.0775	$43.08	$43.10	$43.10
Purchase #6	$33.79	12.503%	$38.0148	$38.01	$38.00	$38.00
Purchase #7	$213.96	5.576%	$225.8904	$225.89	$225.90	$225.90
7 purchase totals =	$863.71		$929.7489	$929.74	$929.80	$929.70