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 $63.78   9.682%   $69.9552   $69.96   $69.95   $70.00  
  Purchase #2 $249.47   6.690%   $266.1595   $266.16   $266.15   $266.20  
  Purchase #3 $20.46   12.813%   $23.0815   $23.08   $23.10   $23.10  
  Purchase #4 $47.91   3.393%   $49.5356   $49.54   $49.55   $49.50  
  Purchase #5 $84.64   12.778%   $95.4553   $95.46   $95.45   $95.50  
  Purchase #6 $214.67   10.256%   $236.6866   $236.69   $236.70   $236.70  
  Purchase #7 $203.99   7.269%   $218.818   $218.82   $218.80   $218.80  
  7 purchase totals = $884.92       $959.6917   $959.71   $959.70   $959.80