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 $232.94   9.669%   $255.463   $255.46   $255.45   $255.50  
  Purchase #2 $39.34   9.143%   $42.9369   $42.94   $42.95   $42.90  
  Purchase #3 $74.79   13.135%   $84.6137   $84.61   $84.60   $84.60  
  Purchase #4 $233.49   13.767%   $265.6346   $265.63   $265.65   $265.60  
  Purchase #5 $230.81   8.505%   $250.4404   $250.44   $250.45   $250.40  
  Purchase #6 $247.58   5.378%   $260.8949   $260.89   $260.90   $260.90  
  Purchase #7 $105.39   7.664%   $113.4671   $113.47   $113.45   $113.50  
  7 purchase totals = $1,164.34       $1,273.4506   $1,273.44   $1,273.45   $1,273.40