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 $208.32   3.241%   $215.0717   $215.07   $215.05   $215.10  
  Purchase #2 $158.81   10.546%   $175.5581   $175.56   $175.55   $175.60  
  Purchase #3 $154.57   11.144%   $171.7953   $171.80   $171.80   $171.80  
  Purchase #4 $92.61   10.588%   $102.4155   $102.42   $102.40   $102.40  
  Purchase #5 $8.33   10.747%   $9.2252   $9.23   $9.25   $9.20  
  Purchase #6 $245.46   6.510%   $261.4394   $261.44   $261.45   $261.40  
  Purchase #7 $83.84   6.228%   $89.0616   $89.06   $89.05   $89.10  
  7 purchase totals = $951.94       $1,024.5668   $1,024.58   $1,024.55   $1,024.60