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 $239.57   9.220%   $261.6584   $261.66   $261.65   $261.70  
  Purchase #2 $49.85   7.397%   $53.5374   $53.54   $53.55   $53.50  
  Purchase #3 $16.97   10.390%   $18.7332   $18.73   $18.75   $18.70  
  Purchase #4 $205.83   7.698%   $221.6748   $221.67   $221.65   $221.70  
  Purchase #5 $230.37   8.250%   $249.3755   $249.38   $249.40   $249.40  
  Purchase #6 $95.95   9.172%   $104.7505   $104.75   $104.75   $104.80  
  Purchase #7 $72.99   3.423%   $75.4884   $75.49   $75.50   $75.50  
  7 purchase totals = $911.53       $985.2182   $985.22   $985.25   $985.30