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 $118.81   3.267%   $122.6915   $122.69   $122.70   $122.70  
  Purchase #2 $131.91   12.354%   $148.2062   $148.21   $148.20   $148.20  
  Purchase #3 $229.86   7.337%   $246.7248   $246.72   $246.70   $246.70  
  Purchase #4 $32.63   8.695%   $35.4672   $35.47   $35.45   $35.50  
  Purchase #5 $148.86   5.603%   $157.2006   $157.20   $157.20   $157.20  
  Purchase #6 $51.82   4.317%   $54.0571   $54.06   $54.05   $54.10  
  Purchase #7 $183.37   7.144%   $196.47   $196.47   $196.45   $196.50  
  7 purchase totals = $897.26       $960.8174   $960.82   $960.75   $960.90