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 $32.53   9.421%   $35.5947   $35.59   $35.60   $35.60  
  Purchase #2 $221.49   3.226%   $228.6353   $228.64   $228.65   $228.60  
  Purchase #3 $91.37   3.541%   $94.6054   $94.61   $94.60   $94.60  
  Purchase #4 $161.99   8.440%   $175.662   $175.66   $175.65   $175.70  
  Purchase #5 $55.89   10.433%   $61.721   $61.72   $61.70   $61.70  
  Purchase #6 $208.57   5.770%   $220.6045   $220.60   $220.60   $220.60  
  Purchase #7 $112.64   7.426%   $121.0046   $121.00   $121.00   $121.00  
  7 purchase totals = $884.48       $937.8275   $937.82   $937.80   $937.80