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 $76.49   13.170%   $86.5637   $86.56   $86.55   $86.60  
  Purchase #2 $239.43   10.263%   $264.0027   $264.00   $264.00   $264.00  
  Purchase #3 $98.91   13.535%   $112.2975   $112.30   $112.30   $112.30  
  Purchase #4 $17.31   5.164%   $18.2039   $18.20   $18.20   $18.20  
  Purchase #5 $58.66   7.436%   $63.022   $63.02   $63.00   $63.00  
  Purchase #6 $6.55   11.285%   $7.2892   $7.29   $7.30   $7.30  
  Purchase #7 $26.95   6.246%   $28.6333   $28.63   $28.65   $28.60  
  7 purchase totals = $524.30       $580.0123   $580.00   $580.00   $580.00