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 $56.57   6.487%   $60.2397   $60.24   $60.25   $60.20  
  Purchase #2 $229.84   6.622%   $245.06   $245.06   $245.05   $245.10  
  Purchase #3 $167.83   9.373%   $183.5607   $183.56   $183.55   $183.60  
  Purchase #4 $124.96   11.432%   $139.2454   $139.25   $139.25   $139.20  
  Purchase #5 $98.87   6.387%   $105.1848   $105.18   $105.20   $105.20  
  Purchase #6 $49.98   6.836%   $53.3966   $53.40   $53.40   $53.40  
  Purchase #7 $199.42   4.571%   $208.5355   $208.54   $208.55   $208.50  
  7 purchase totals = $927.47       $995.2227   $995.23   $995.25   $995.20