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 $205.76   8.462%   $223.1714   $223.17   $223.15   $223.20  
  Purchase #2 $234.25   4.830%   $245.5643   $245.56   $245.55   $245.60  
  Purchase #3 $73.32   5.861%   $77.6173   $77.62   $77.60   $77.60  
  Purchase #4 $166.75   9.826%   $183.1349   $183.13   $183.15   $183.10  
  Purchase #5 $231.42   8.295%   $250.6163   $250.62   $250.60   $250.60  
  Purchase #6 $148.67   13.592%   $168.8772   $168.88   $168.90   $168.90  
  Purchase #7 $235.48   10.195%   $259.4872   $259.49   $259.50   $259.50  
  7 purchase totals = $1,295.65       $1,408.4686   $1,408.47   $1,408.45   $1,408.50