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 $109.48   9.337%   $119.7021   $119.70   $119.70   $119.70  
  Purchase #2 $250.88   4.111%   $261.1937   $261.19   $261.20   $261.20  
  Purchase #3 $111.76   12.589%   $125.8295   $125.83   $125.85   $125.80  
  Purchase #4 $250.44   7.446%   $269.0878   $269.09   $269.10   $269.10  
  Purchase #5 $245.34   5.534%   $258.9171   $258.92   $258.90   $258.90  
  Purchase #6 $175.72   12.364%   $197.446   $197.45   $197.45   $197.40  
  Purchase #7 $51.59   4.141%   $53.7263   $53.73   $53.75   $53.70  
  7 purchase totals = $1,195.21       $1,285.9025   $1,285.91   $1,285.95   $1,285.80