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 $54.41   12.696%   $61.3179   $61.32   $61.30   $61.30  
  Purchase #2 $231.92   4.606%   $242.6022   $242.60   $242.60   $242.60  
  Purchase #3 $40.29   11.421%   $44.8915   $44.89   $44.90   $44.90  
  Purchase #4 $122.56   3.371%   $126.6915   $126.69   $126.70   $126.70  
  Purchase #5 $156.90   4.226%   $163.5306   $163.53   $163.55   $163.50  
  Purchase #6 $146.84   8.609%   $159.4815   $159.48   $159.50   $159.50  
  Purchase #7 $15.66   11.474%   $17.4568   $17.46   $17.45   $17.50  
  7 purchase totals = $768.58       $815.9720   $815.97   $816.00   $816.00