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 $246.25   8.609%   $267.4497   $267.45   $267.45   $267.40  
  Purchase #2 $29.31   3.169%   $30.2388   $30.24   $30.25   $30.20  
  Purchase #3 $232.70   6.221%   $247.1763   $247.18   $247.20   $247.20  
  Purchase #4 $78.65   8.787%   $85.561   $85.56   $85.55   $85.60  
  Purchase #5 $242.27   5.354%   $255.2411   $255.24   $255.25   $255.20  
  Purchase #6 $236.94   10.282%   $261.3022   $261.30   $261.30   $261.30  
  Purchase #7 $192.44   9.353%   $210.4389   $210.44   $210.45   $210.40  
  7 purchase totals = $1,258.56       $1,357.4080   $1,357.41   $1,357.45   $1,357.30