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 $65.79   5.683%   $69.5288   $69.53   $69.55   $69.50  
  Purchase #2 $14.46   11.851%   $16.1737   $16.17   $16.15   $16.20  
  Purchase #3 $158.38   11.526%   $176.6349   $176.63   $176.65   $176.60  
  Purchase #4 $109.68   11.298%   $122.0716   $122.07   $122.05   $122.10  
  Purchase #5 $245.54   4.328%   $256.167   $256.17   $256.15   $256.20  
  Purchase #6 $151.60   8.724%   $164.8256   $164.83   $164.85   $164.80  
  Purchase #7 $184.37   10.416%   $203.574   $203.57   $203.55   $203.60  
  7 purchase totals = $929.82       $1,008.9756   $1,008.97   $1,008.95   $1,009.00