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 $58.76   13.169%   $66.4981   $66.50   $66.50   $66.50  
  Purchase #2 $179.79   8.773%   $195.563   $195.56   $195.55   $195.60  
  Purchase #3 $127.32   6.843%   $136.0325   $136.03   $136.05   $136.00  
  Purchase #4 $104.99   3.330%   $108.4862   $108.49   $108.50   $108.50  
  Purchase #5 $81.33   7.274%   $87.2459   $87.25   $87.25   $87.20  
  Purchase #6 $244.88   13.696%   $278.4188   $278.42   $278.40   $278.40  
  Purchase #7 $168.38   8.220%   $182.2208   $182.22   $182.20   $182.20  
  7 purchase totals = $965.45       $1,054.4653   $1,054.47   $1,054.45   $1,054.40