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 $229.91   9.842%   $252.5377   $252.54   $252.55   $252.50  
  Purchase #2 $208.58   3.476%   $215.8302   $215.83   $215.85   $215.80  
  Purchase #3 $16.94   8.583%   $18.394   $18.39   $18.40   $18.40  
  Purchase #4 $123.80   7.668%   $133.293   $133.29   $133.30   $133.30  
  Purchase #5 $240.62   8.856%   $261.9293   $261.93   $261.95   $261.90  
  Purchase #6 $132.90   9.341%   $145.3142   $145.31   $145.30   $145.30  
  Purchase #7 $248.46   9.498%   $272.0587   $272.06   $272.05   $272.10  
  7 purchase totals = $1,201.21       $1,299.3571   $1,299.35   $1,299.40   $1,299.30