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 $84.33   13.697%   $95.8807   $95.88   $95.90   $95.90  
  Purchase #2 $77.81   7.142%   $83.3672   $83.37   $83.35   $83.40  
  Purchase #3 $66.25   8.655%   $71.9839   $71.98   $72.00   $72.00  
  Purchase #4 $184.32   12.607%   $207.5572   $207.56   $207.55   $207.60  
  Purchase #5 $139.69   4.829%   $146.4356   $146.44   $146.45   $146.40  
  Purchase #6 $107.84   13.378%   $122.2668   $122.27   $122.25   $122.30  
  Purchase #7 $170.83   10.397%   $188.5912   $188.59   $188.60   $188.60  
  7 purchase totals = $831.07       $916.0826   $916.09   $916.10   $916.20