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 $243.84   13.453%   $276.6438   $276.64   $276.65   $276.60  
  Purchase #2 $169.43   10.517%   $187.249   $187.25   $187.25   $187.20  
  Purchase #3 $240.66   7.724%   $259.2486   $259.25   $259.25   $259.20  
  Purchase #4 $26.78   13.551%   $30.409   $30.41   $30.40   $30.40  
  Purchase #5 $113.73   8.595%   $123.5051   $123.51   $123.50   $123.50  
  Purchase #6 $173.81   12.536%   $195.5988   $195.60   $195.60   $195.60  
  Purchase #7 $34.57   12.851%   $39.0126   $39.01   $39.00   $39.00  
  7 purchase totals = $1,002.82       $1,111.6669   $1,111.67   $1,111.65   $1,111.50