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 $208.63   9.356%   $228.1494   $228.15   $228.15   $228.10  
  Purchase #2 $114.77   10.223%   $126.5029   $126.50   $126.50   $126.50  
  Purchase #3 $49.55   9.376%   $54.1958   $54.20   $54.20   $54.20  
  Purchase #4 $239.58   8.263%   $259.3765   $259.38   $259.40   $259.40  
  Purchase #5 $57.88   6.257%   $61.5016   $61.50   $61.50   $61.50  
  Purchase #6 $189.35   12.385%   $212.801   $212.80   $212.80   $212.80  
  Purchase #7 $12.70   7.859%   $13.6981   $13.70   $13.70   $13.70  
  7 purchase totals = $872.46       $956.2253   $956.23   $956.25   $956.20