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 $96.56   10.357%   $106.5607   $106.56   $106.55   $106.60  
  Purchase #2 $209.88   12.589%   $236.3018   $236.30   $236.30   $236.30  
  Purchase #3 $72.91   7.564%   $78.4249   $78.42   $78.40   $78.40  
  Purchase #4 $62.30   12.256%   $69.9355   $69.94   $69.95   $69.90  
  Purchase #5 $40.64   9.355%   $44.4419   $44.44   $44.45   $44.40  
  Purchase #6 $44.32   11.693%   $49.5023   $49.50   $49.50   $49.50  
  Purchase #7 $175.70   6.311%   $186.7884   $186.79   $186.80   $186.80  
  7 purchase totals = $702.31       $771.9555   $771.95   $771.95   $771.90