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 $32.42   5.681%   $34.2618   $34.26   $34.25   $34.30  
  Purchase #2 $200.37   8.131%   $216.6621   $216.66   $216.65   $216.70  
  Purchase #3 $201.49   10.448%   $222.5417   $222.54   $222.55   $222.50  
  Purchase #4 $229.59   12.305%   $257.841   $257.84   $257.85   $257.80  
  Purchase #5 $224.94   10.293%   $248.0931   $248.09   $248.10   $248.10  
  Purchase #6 $17.80   13.210%   $20.1514   $20.15   $20.15   $20.20  
  Purchase #7 $244.32   9.626%   $267.8382   $267.84   $267.85   $267.80  
  7 purchase totals = $1,150.93       $1,267.3893   $1,267.38   $1,267.40   $1,267.40