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 $111.95   11.297%   $124.597   $124.60   $124.60   $124.60  
  Purchase #2 $113.84   9.759%   $124.9496   $124.95   $124.95   $124.90  
  Purchase #3 $77.54   9.715%   $85.073   $85.07   $85.05   $85.10  
  Purchase #4 $162.99   5.778%   $172.4076   $172.41   $172.40   $172.40  
  Purchase #5 $149.94   8.703%   $162.9893   $162.99   $163.00   $163.00  
  Purchase #6 $206.91   4.124%   $215.443   $215.44   $215.45   $215.40  
  Purchase #7 $135.99   13.524%   $154.3813   $154.38   $154.40   $154.40  
  7 purchase totals = $959.16       $1,039.8408   $1,039.84   $1,039.85   $1,039.80