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 $183.71   12.397%   $206.4845   $206.48   $206.50   $206.50  
  Purchase #2 $249.76   10.383%   $275.6926   $275.69   $275.70   $275.70  
  Purchase #3 $6.67   8.609%   $7.2442   $7.24   $7.25   $7.20  
  Purchase #4 $239.97   9.291%   $262.2656   $262.27   $262.25   $262.30  
  Purchase #5 $75.42   11.498%   $84.0918   $84.09   $84.10   $84.10  
  Purchase #6 $210.88   5.868%   $223.2544   $223.25   $223.25   $223.30  
  Purchase #7 $135.92   7.202%   $145.709   $145.71   $145.70   $145.70  
  7 purchase totals = $1,102.33       $1,204.7421   $1,204.73   $1,204.75   $1,204.80