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 $196.29   3.751%   $203.6528   $203.65   $203.65   $203.70  
  Purchase #2 $121.25   9.229%   $132.4402   $132.44   $132.45   $132.40  
  Purchase #3 $237.51   7.670%   $255.727   $255.73   $255.75   $255.70  
  Purchase #4 $247.64   5.673%   $261.6886   $261.69   $261.70   $261.70  
  Purchase #5 $222.51   12.352%   $249.9944   $249.99   $250.00   $250.00  
  Purchase #6 $207.82   11.379%   $231.4678   $231.47   $231.45   $231.50  
  Purchase #7 $152.51   7.746%   $164.3234   $164.32   $164.30   $164.30  
  7 purchase totals = $1,385.53       $1,499.2942   $1,499.29   $1,499.30   $1,499.30