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 $53.79   11.194%   $59.8113   $59.81   $59.80   $59.80  
  Purchase #2 $249.32   4.790%   $261.2624   $261.26   $261.25   $261.30  
  Purchase #3 $107.72   12.631%   $121.3261   $121.33   $121.35   $121.30  
  Purchase #4 $67.70   8.276%   $73.3029   $73.30   $73.30   $73.30  
  Purchase #5 $134.65   4.503%   $140.7133   $140.71   $140.70   $140.70  
  Purchase #6 $6.28   4.351%   $6.5532   $6.55   $6.55   $6.60  
  Purchase #7 $156.85   10.195%   $172.8409   $172.84   $172.85   $172.80  
  7 purchase totals = $776.31       $835.8101   $835.80   $835.80   $835.80