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 $22.77   12.612%   $25.6418   $25.64   $25.65   $25.60  
  Purchase #2 $206.26   8.597%   $223.9922   $223.99   $224.00   $224.00  
  Purchase #3 $119.91   9.804%   $131.666   $131.67   $131.65   $131.70  
  Purchase #4 $169.84   10.239%   $187.2299   $187.23   $187.25   $187.20  
  Purchase #5 $158.80   9.189%   $173.3921   $173.39   $173.40   $173.40  
  Purchase #6 $185.50   10.767%   $205.4728   $205.47   $205.45   $205.50  
  Purchase #7 $78.60   3.609%   $81.4367   $81.44   $81.45   $81.40  
  7 purchase totals = $941.68       $1,028.8315   $1,028.83   $1,028.85   $1,028.80