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 $49.76   5.208%   $52.3515   $52.35   $52.35   $52.40  
  Purchase #2 $241.42   12.108%   $270.6511   $270.65   $270.65   $270.70  
  Purchase #3 $108.36   5.639%   $114.4704   $114.47   $114.45   $114.50  
  Purchase #4 $204.75   5.440%   $215.8884   $215.89   $215.90   $215.90  
  Purchase #5 $23.72   4.857%   $24.8721   $24.87   $24.85   $24.90  
  Purchase #6 $24.67   8.262%   $26.7082   $26.71   $26.70   $26.70  
  Purchase #7 $8.59   10.263%   $9.4716   $9.47   $9.45   $9.50  
  7 purchase totals = $661.27       $714.4133   $714.41   $714.35   $714.60