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 $14.78   8.393%   $16.0205   $16.02   $16.00   $16.00  
  Purchase #2 $214.93   8.414%   $233.0142   $233.01   $233.00   $233.00  
  Purchase #3 $184.65   6.293%   $196.27   $196.27   $196.25   $196.30  
  Purchase #4 $69.68   12.134%   $78.135   $78.14   $78.15   $78.10  
  Purchase #5 $134.46   7.419%   $144.4356   $144.44   $144.45   $144.40  
  Purchase #6 $61.53   10.517%   $68.0011   $68.00   $68.00   $68.00  
  Purchase #7 $26.85   8.614%   $29.1629   $29.16   $29.15   $29.20  
  7 purchase totals = $706.88       $765.0393   $765.04   $765.00   $765.00