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 $84.63   13.267%   $95.8579   $95.86   $95.85   $95.90  
  Purchase #2 $155.31   13.235%   $175.8653   $175.87   $175.85   $175.90  
  Purchase #3 $31.48   13.553%   $35.7465   $35.75   $35.75   $35.70  
  Purchase #4 $105.61   6.719%   $112.7059   $112.71   $112.70   $112.70  
  Purchase #5 $57.85   10.737%   $64.0614   $64.06   $64.05   $64.10  
  Purchase #6 $106.31   13.152%   $120.2919   $120.29   $120.30   $120.30  
  Purchase #7 $50.50   11.173%   $56.1424   $56.14   $56.15   $56.10  
  7 purchase totals = $591.69       $660.6713   $660.68   $660.65   $660.70