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 $224.60   11.397%   $250.1977   $250.20   $250.20   $250.20  
  Purchase #2 $38.39   13.848%   $43.7062   $43.71   $43.70   $43.70  
  Purchase #3 $176.56   3.226%   $182.2558   $182.26   $182.25   $182.30  
  Purchase #4 $212.87   5.489%   $224.5544   $224.55   $224.55   $224.60  
  Purchase #5 $8.66   5.779%   $9.1605   $9.16   $9.15   $9.20  
  Purchase #6 $209.51   13.268%   $237.3078   $237.31   $237.30   $237.30  
  Purchase #7 $57.69   7.626%   $62.0894   $62.09   $62.10   $62.10  
  7 purchase totals = $928.28       $1,009.2718   $1,009.28   $1,009.25   $1,009.40