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 $108.58   6.149%   $115.2566   $115.26   $115.25   $115.30  
  Purchase #2 $134.69   5.756%   $142.4428   $142.44   $142.45   $142.40  
  Purchase #3 $139.94   13.537%   $158.8837   $158.88   $158.90   $158.90  
  Purchase #4 $182.39   5.525%   $192.467   $192.47   $192.45   $192.50  
  Purchase #5 $70.87   11.417%   $78.9612   $78.96   $78.95   $79.00  
  Purchase #6 $228.89   4.515%   $239.2244   $239.22   $239.20   $239.20  
  Purchase #7 $23.88   11.632%   $26.6577   $26.66   $26.65   $26.70  
  7 purchase totals = $889.24       $953.8934   $953.89   $953.85   $954.00