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 $23.54   10.418%   $25.9924   $25.99   $26.00   $26.00  
  Purchase #2 $145.76   9.154%   $159.1029   $159.10   $159.10   $159.10  
  Purchase #3 $230.56   13.525%   $261.7432   $261.74   $261.75   $261.70  
  Purchase #4 $181.80   4.680%   $190.3082   $190.31   $190.30   $190.30  
  Purchase #5 $82.54   6.726%   $88.0916   $88.09   $88.10   $88.10  
  Purchase #6 $59.67   11.796%   $66.7087   $66.71   $66.70   $66.70  
  Purchase #7 $157.48   11.839%   $176.1241   $176.12   $176.10   $176.10  
  7 purchase totals = $881.35       $968.0711   $968.06   $968.05   $968.00