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 $116.95   6.655%   $124.733   $124.73   $124.75   $124.70  
  Purchase #2 $214.57   4.696%   $224.6462   $224.65   $224.65   $224.60  
  Purchase #3 $24.36   10.395%   $26.8922   $26.89   $26.90   $26.90  
  Purchase #4 $211.78   3.345%   $218.864   $218.86   $218.85   $218.90  
  Purchase #5 $118.79   6.247%   $126.2108   $126.21   $126.20   $126.20  
  Purchase #6 $5.69   8.311%   $6.1629   $6.16   $6.15   $6.20  
  Purchase #7 $205.42   12.709%   $231.5268   $231.53   $231.55   $231.50  
  7 purchase totals = $897.56       $959.0359   $959.03   $959.05   $959.00