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 $186.79   11.660%   $208.5697   $208.57   $208.55   $208.60  
  Purchase #2 $35.33   6.748%   $37.7141   $37.71   $37.70   $37.70  
  Purchase #3 $140.31   10.514%   $155.0622   $155.06   $155.05   $155.10  
  Purchase #4 $60.75   4.114%   $63.2493   $63.25   $63.25   $63.20  
  Purchase #5 $89.27   7.858%   $96.2848   $96.28   $96.30   $96.30  
  Purchase #6 $161.84   8.448%   $175.5122   $175.51   $175.50   $175.50  
  Purchase #7 $179.99   7.122%   $192.8089   $192.81   $192.80   $192.80  
  7 purchase totals = $854.28       $929.2012   $929.19   $929.15   $929.20