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 $245.92   6.400%   $261.6589   $261.66   $261.65   $261.70  
  Purchase #2 $60.30   4.507%   $63.0177   $63.02   $63.00   $63.00  
  Purchase #3 $138.67   4.329%   $144.673   $144.67   $144.65   $144.70  
  Purchase #4 $108.66   9.141%   $118.5926   $118.59   $118.60   $118.60  
  Purchase #5 $6.45   8.611%   $7.0054   $7.01   $7.00   $7.00  
  Purchase #6 $76.94   12.735%   $86.7383   $86.74   $86.75   $86.70  
  Purchase #7 $102.77   8.572%   $111.5794   $111.58   $111.60   $111.60  
  7 purchase totals = $739.71       $793.2653   $793.27   $793.25   $793.30