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 $117.44   6.828%   $125.4588   $125.46   $125.45   $125.50  
  Purchase #2 $67.27   6.681%   $71.7643   $71.76   $71.75   $71.80  
  Purchase #3 $247.39   11.237%   $275.1892   $275.19   $275.20   $275.20  
  Purchase #4 $171.35   8.478%   $185.8771   $185.88   $185.90   $185.90  
  Purchase #5 $52.55   5.859%   $55.6289   $55.63   $55.65   $55.60  
  Purchase #6 $136.32   10.340%   $150.4155   $150.42   $150.40   $150.40  
  Purchase #7 $16.55   5.762%   $17.5036   $17.50   $17.50   $17.50  
  7 purchase totals = $808.87       $881.8374   $881.84   $881.85   $881.90