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 $8.94   3.370%   $9.2413   $9.24   $9.25   $9.20  
  Purchase #2 $106.60   3.641%   $110.4813   $110.48   $110.50   $110.50  
  Purchase #3 $78.47   10.487%   $86.6991   $86.70   $86.70   $86.70  
  Purchase #4 $249.87   12.256%   $280.4941   $280.49   $280.50   $280.50  
  Purchase #5 $138.37   13.789%   $157.4498   $157.45   $157.45   $157.40  
  Purchase #6 $10.76   9.317%   $11.7625   $11.76   $11.75   $11.80  
  Purchase #7 $75.53   7.128%   $80.9138   $80.91   $80.90   $80.90  
  7 purchase totals = $668.54       $737.0419   $737.03   $737.05   $737.00