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 $30.79   6.258%   $32.7168   $32.72   $32.70   $32.70  
  Purchase #2 $148.30   10.591%   $164.0065   $164.01   $164.00   $164.00  
  Purchase #3 $119.89   5.211%   $126.1375   $126.14   $126.15   $126.10  
  Purchase #4 $223.76   8.241%   $242.2001   $242.20   $242.20   $242.20  
  Purchase #5 $149.25   4.528%   $156.008   $156.01   $156.00   $156.00  
  Purchase #6 $49.28   3.611%   $51.0595   $51.06   $51.05   $51.10  
  Purchase #7 $183.43   3.794%   $190.3893   $190.39   $190.40   $190.40  
  7 purchase totals = $904.70       $962.5177   $962.53   $962.50   $962.50