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 $58.25   8.834%   $63.3958   $63.40   $63.40   $63.40  
  Purchase #2 $7.91   4.591%   $8.2731   $8.27   $8.25   $8.30  
  Purchase #3 $101.28   6.264%   $107.6242   $107.62   $107.60   $107.60  
  Purchase #4 $238.86   4.558%   $249.7472   $249.75   $249.75   $249.70  
  Purchase #5 $96.75   12.695%   $109.0324   $109.03   $109.05   $109.00  
  Purchase #6 $242.78   12.450%   $273.0061   $273.01   $273.00   $273.00  
  Purchase #7 $231.28   12.853%   $261.0064   $261.01   $261.00   $261.00  
  7 purchase totals = $977.11       $1,072.0852   $1,072.09   $1,072.05   $1,072.00