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 $214.64   9.330%   $234.6659   $234.67   $234.65   $234.70  
  Purchase #2 $189.49   11.812%   $211.8726   $211.87   $211.85   $211.90  
  Purchase #3 $56.78   7.287%   $60.9176   $60.92   $60.90   $60.90  
  Purchase #4 $164.77   9.286%   $180.0705   $180.07   $180.05   $180.10  
  Purchase #5 $182.73   11.611%   $203.9468   $203.95   $203.95   $203.90  
  Purchase #6 $241.93   8.131%   $261.6013   $261.60   $261.60   $261.60  
  Purchase #7 $154.95   3.781%   $160.8087   $160.81   $160.80   $160.80  
  7 purchase totals = $1,205.29       $1,313.8834   $1,313.89   $1,313.80   $1,313.90