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 $231.49   7.622%   $249.1342   $249.13   $249.15   $249.10  
  Purchase #2 $73.68   5.314%   $77.5954   $77.60   $77.60   $77.60  
  Purchase #3 $125.79   10.244%   $138.6759   $138.68   $138.70   $138.70  
  Purchase #4 $207.41   10.632%   $229.4618   $229.46   $229.45   $229.50  
  Purchase #5 $242.43   8.347%   $262.6656   $262.67   $262.65   $262.70  
  Purchase #6 $89.65   7.840%   $96.6786   $96.68   $96.70   $96.70  
  Purchase #7 $11.80   10.742%   $13.0676   $13.07   $13.05   $13.10  
  7 purchase totals = $982.25       $1,067.2791   $1,067.29   $1,067.30   $1,067.40