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 $230.47   13.457%   $261.4843   $261.48   $261.50   $261.50  
  Purchase #2 $127.94   11.207%   $142.2782   $142.28   $142.30   $142.30  
  Purchase #3 $121.49   10.624%   $134.3971   $134.40   $134.40   $134.40  
  Purchase #4 $218.59   13.517%   $248.1368   $248.14   $248.15   $248.10  
  Purchase #5 $206.93   13.867%   $235.625   $235.63   $235.65   $235.60  
  Purchase #6 $209.77   8.851%   $228.3367   $228.34   $228.35   $228.30  
  Purchase #7 $169.89   7.239%   $182.1883   $182.19   $182.20   $182.20  
  7 purchase totals = $1,285.08       $1,432.4464   $1,432.46   $1,432.55   $1,432.40