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 $24.58   8.119%   $26.5757   $26.58   $26.60   $26.60  
  Purchase #2 $211.70   8.517%   $229.7305   $229.73   $229.75   $229.70  
  Purchase #3 $64.56   7.832%   $69.6163   $69.62   $69.60   $69.60  
  Purchase #4 $227.86   10.268%   $251.2567   $251.26   $251.25   $251.30  
  Purchase #5 $225.46   3.311%   $232.925   $232.93   $232.95   $232.90  
  Purchase #6 $64.38   9.122%   $70.2527   $70.25   $70.25   $70.30  
  Purchase #7 $102.66   3.113%   $105.8558   $105.86   $105.85   $105.90  
  7 purchase totals = $921.20       $986.2127   $986.23   $986.25   $986.30