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 $231.45   13.743%   $263.2582   $263.26   $263.25   $263.30  
  Purchase #2 $248.38   5.437%   $261.8844   $261.88   $261.90   $261.90  
  Purchase #3 $93.70   11.168%   $104.1644   $104.16   $104.15   $104.20  
  Purchase #4 $74.80   3.213%   $77.2033   $77.20   $77.20   $77.20  
  Purchase #5 $118.83   13.874%   $135.3165   $135.32   $135.30   $135.30  
  Purchase #6 $163.28   5.115%   $171.6318   $171.63   $171.65   $171.60  
  Purchase #7 $63.98   12.713%   $72.1138   $72.11   $72.10   $72.10  
  7 purchase totals = $994.42       $1,085.5724   $1,085.56   $1,085.55   $1,085.60