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 $246.83   10.801%   $273.4901   $273.49   $273.50   $273.50  
  Purchase #2 $159.71   7.354%   $171.4551   $171.46   $171.45   $171.50  
  Purchase #3 $42.47   8.302%   $45.9959   $46.00   $46.00   $46.00  
  Purchase #4 $234.48   5.296%   $246.8981   $246.90   $246.90   $246.90  
  Purchase #5 $149.25   13.556%   $169.4823   $169.48   $169.50   $169.50  
  Purchase #6 $202.32   10.711%   $223.9905   $223.99   $224.00   $224.00  
  Purchase #7 $228.87   7.120%   $245.1655   $245.17   $245.15   $245.20  
  7 purchase totals = $1,263.93       $1,376.4775   $1,376.49   $1,376.50   $1,376.60