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 $55.71   7.773%   $60.0403   $60.04   $60.05   $60.00  
  Purchase #2 $78.99   6.388%   $84.0359   $84.04   $84.05   $84.00  
  Purchase #3 $94.81   5.336%   $99.8691   $99.87   $99.85   $99.90  
  Purchase #4 $23.87   11.811%   $26.6893   $26.69   $26.70   $26.70  
  Purchase #5 $184.85   6.201%   $196.3125   $196.31   $196.30   $196.30  
  Purchase #6 $76.72   3.425%   $79.3477   $79.35   $79.35   $79.30  
  Purchase #7 $140.61   5.789%   $148.7499   $148.75   $148.75   $148.70  
  7 purchase totals = $655.56       $695.0447   $695.05   $695.05   $694.90