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 $55.70   11.168%   $61.9206   $61.92   $61.90   $61.90  
  Purchase #2 $230.46   13.663%   $261.9477   $261.95   $261.95   $261.90  
  Purchase #3 $160.49   5.102%   $168.6782   $168.68   $168.70   $168.70  
  Purchase #4 $157.56   13.848%   $179.3789   $179.38   $179.40   $179.40  
  Purchase #5 $42.69   7.162%   $45.7475   $45.75   $45.75   $45.70  
  Purchase #6 $108.57   12.386%   $122.0175   $122.02   $122.00   $122.00  
  Purchase #7 $171.32   3.576%   $177.4464   $177.45   $177.45   $177.40  
  7 purchase totals = $926.79       $1,017.1368   $1,017.15   $1,017.15   $1,017.00