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 $248.47   13.804%   $282.7688   $282.77   $282.75   $282.80  
  Purchase #2 $34.44   8.579%   $37.3946   $37.39   $37.40   $37.40  
  Purchase #3 $107.56   8.782%   $117.0059   $117.01   $117.00   $117.00  
  Purchase #4 $16.80   11.226%   $18.686   $18.69   $18.70   $18.70  
  Purchase #5 $78.44   4.476%   $81.951   $81.95   $81.95   $82.00  
  Purchase #6 $68.93   13.110%   $77.9667   $77.97   $77.95   $78.00  
  Purchase #7 $127.42   13.771%   $144.967   $144.97   $144.95   $145.00  
  7 purchase totals = $682.06       $760.7400   $760.75   $760.70   $760.90