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 $237.95   12.217%   $267.0204   $267.02   $267.00   $267.00  
  Purchase #2 $31.81   3.649%   $32.9707   $32.97   $32.95   $33.00  
  Purchase #3 $215.71   7.863%   $232.6713   $232.67   $232.65   $232.70  
  Purchase #4 $187.61   13.778%   $213.4589   $213.46   $213.45   $213.50  
  Purchase #5 $71.81   8.490%   $77.9067   $77.91   $77.90   $77.90  
  Purchase #6 $104.76   3.784%   $108.7241   $108.72   $108.70   $108.70  
  Purchase #7 $21.80   4.292%   $22.7357   $22.74   $22.75   $22.70  
  7 purchase totals = $871.45       $955.4878   $955.49   $955.40   $955.50