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 $205.63   6.607%   $219.216   $219.22   $219.20   $219.20  
  Purchase #2 $56.99   7.223%   $61.1064   $61.11   $61.10   $61.10  
  Purchase #3 $232.84   12.571%   $262.1103   $262.11   $262.10   $262.10  
  Purchase #4 $75.61   3.448%   $78.217   $78.22   $78.20   $78.20  
  Purchase #5 $26.95   13.807%   $30.671   $30.67   $30.65   $30.70  
  Purchase #6 $92.75   7.208%   $99.4354   $99.44   $99.45   $99.40  
  Purchase #7 $40.41   7.413%   $43.4056   $43.41   $43.40   $43.40  
  7 purchase totals = $731.18       $794.1617   $794.18   $794.10   $794.10