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 $59.75   6.792%   $63.8082   $63.81   $63.80   $63.80  
  Purchase #2 $86.97   6.867%   $92.9422   $92.94   $92.95   $92.90  
  Purchase #3 $135.67   3.138%   $139.9273   $139.93   $139.95   $139.90  
  Purchase #4 $248.88   13.410%   $282.2548   $282.25   $282.25   $282.30  
  Purchase #5 $249.87   9.618%   $273.9025   $273.90   $273.90   $273.90  
  Purchase #6 $201.50   7.180%   $215.9677   $215.97   $215.95   $216.00  
  Purchase #7 $239.66   8.484%   $259.9928   $259.99   $260.00   $260.00  
  7 purchase totals = $1,222.30       $1,328.7955   $1,328.79   $1,328.80   $1,328.80