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 $229.61   8.393%   $248.8812   $248.88   $248.90   $248.90  
  Purchase #2 $197.93   5.406%   $208.6301   $208.63   $208.65   $208.60  
  Purchase #3 $35.62   7.394%   $38.2537   $38.25   $38.25   $38.30  
  Purchase #4 $203.79   3.414%   $210.7474   $210.75   $210.75   $210.70  
  Purchase #5 $235.64   12.527%   $265.1586   $265.16   $265.15   $265.20  
  Purchase #6 $203.56   6.110%   $215.9975   $216.00   $216.00   $216.00  
  Purchase #7 $119.85   12.641%   $135.0002   $135.00   $135.00   $135.00  
  7 purchase totals = $1,226.00       $1,322.6687   $1,322.67   $1,322.70   $1,322.70