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 $111.58   13.167%   $126.2717   $126.27   $126.25   $126.30  
  Purchase #2 $109.32   8.586%   $118.7062   $118.71   $118.70   $118.70  
  Purchase #3 $76.61   9.308%   $83.7409   $83.74   $83.75   $83.70  
  Purchase #4 $20.95   12.850%   $23.6421   $23.64   $23.65   $23.60  
  Purchase #5 $221.39   6.806%   $236.4578   $236.46   $236.45   $236.50  
  Purchase #6 $232.65   7.455%   $249.9941   $249.99   $250.00   $250.00  
  Purchase #7 $216.76   8.327%   $234.8096   $234.81   $234.80   $234.80  
  7 purchase totals = $989.26       $1,073.6224   $1,073.62   $1,073.60   $1,073.60