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 $112.78   9.689%   $123.7073   $123.71   $123.70   $123.70  
  Purchase #2 $72.79   7.622%   $78.3381   $78.34   $78.35   $78.30  
  Purchase #3 $182.79   8.574%   $198.4624   $198.46   $198.45   $198.50  
  Purchase #4 $250.32   10.492%   $276.5836   $276.58   $276.60   $276.60  
  Purchase #5 $9.34   4.719%   $9.7808   $9.78   $9.80   $9.80  
  Purchase #6 $27.90   7.625%   $30.0274   $30.03   $30.05   $30.00  
  Purchase #7 $69.78   7.307%   $74.8788   $74.88   $74.90   $74.90  
  7 purchase totals = $725.70       $791.7784   $791.78   $791.85   $791.80