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 $83.58   3.566%   $86.5605   $86.56   $86.55   $86.60  
  Purchase #2 $173.45   13.458%   $196.7929   $196.79   $196.80   $196.80  
  Purchase #3 $114.50   9.363%   $125.2206   $125.22   $125.20   $125.20  
  Purchase #4 $201.81   3.801%   $209.4808   $209.48   $209.50   $209.50  
  Purchase #5 $146.66   8.731%   $159.4649   $159.46   $159.45   $159.50  
  Purchase #6 $72.81   4.541%   $76.1163   $76.12   $76.10   $76.10  
  Purchase #7 $28.78   5.719%   $30.4259   $30.43   $30.45   $30.40  
  7 purchase totals = $821.59       $884.0619   $884.06   $884.05   $884.10