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 $23.60   12.354%   $26.5155   $26.52   $26.50   $26.50  
  Purchase #2 $249.54   4.859%   $261.6651   $261.67   $261.65   $261.70  
  Purchase #3 $133.42   7.411%   $143.3078   $143.31   $143.30   $143.30  
  Purchase #4 $249.51   5.595%   $263.4701   $263.47   $263.45   $263.50  
  Purchase #5 $218.36   13.304%   $247.4106   $247.41   $247.40   $247.40  
  Purchase #6 $243.47   8.630%   $264.4815   $264.48   $264.50   $264.50  
  Purchase #7 $136.67   4.355%   $142.622   $142.62   $142.60   $142.60  
  7 purchase totals = $1,254.57       $1,349.4726   $1,349.48   $1,349.40   $1,349.50