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 $224.69   8.292%   $243.3213   $243.32   $243.30   $243.30  
  Purchase #2 $118.64   6.529%   $126.386   $126.39   $126.40   $126.40  
  Purchase #3 $249.31   12.192%   $279.7059   $279.71   $279.70   $279.70  
  Purchase #4 $176.59   5.822%   $186.8711   $186.87   $186.85   $186.90  
  Purchase #5 $243.81   6.434%   $259.4967   $259.50   $259.50   $259.50  
  Purchase #6 $55.70   7.730%   $60.0056   $60.01   $60.00   $60.00  
  Purchase #7 $248.66   8.859%   $270.6888   $270.69   $270.70   $270.70  
  7 purchase totals = $1,317.40       $1,426.4754   $1,426.49   $1,426.45   $1,426.50