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 $62.90   13.627%   $71.4714   $71.47   $71.45   $71.50  
  Purchase #2 $188.25   9.622%   $206.3634   $206.36   $206.35   $206.40  
  Purchase #3 $134.48   10.393%   $148.4565   $148.46   $148.45   $148.50  
  Purchase #4 $57.98   3.649%   $60.0957   $60.10   $60.10   $60.10  
  Purchase #5 $41.73   13.204%   $47.24   $47.24   $47.25   $47.20  
  Purchase #6 $71.32   13.763%   $81.1358   $81.14   $81.15   $81.10  
  Purchase #7 $115.87   6.695%   $123.6275   $123.63   $123.65   $123.60  
  7 purchase totals = $672.53       $738.3903   $738.40   $738.40   $738.40