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 $183.49   6.624%   $195.6444   $195.64   $195.65   $195.60  
  Purchase #2 $235.34   11.256%   $261.8299   $261.83   $261.85   $261.80  
  Purchase #3 $227.47   8.769%   $247.4168   $247.42   $247.40   $247.40  
  Purchase #4 $101.91   10.787%   $112.903   $112.90   $112.90   $112.90  
  Purchase #5 $29.64   4.737%   $31.044   $31.04   $31.05   $31.00  
  Purchase #6 $53.85   7.266%   $57.7627   $57.76   $57.75   $57.80  
  Purchase #7 $208.55   12.795%   $235.234   $235.23   $235.25   $235.20  
  7 purchase totals = $1,040.25       $1,141.8348   $1,141.82   $1,141.85   $1,141.70