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 $237.78   11.681%   $265.5551   $265.56   $265.55   $265.60  
  Purchase #2 $20.87   3.515%   $21.6036   $21.60   $21.60   $21.60  
  Purchase #3 $176.51   3.381%   $182.4778   $182.48   $182.50   $182.50  
  Purchase #4 $64.74   11.836%   $72.4026   $72.40   $72.40   $72.40  
  Purchase #5 $98.92   3.823%   $102.7017   $102.70   $102.70   $102.70  
  Purchase #6 $96.69   11.332%   $107.6469   $107.65   $107.65   $107.60  
  Purchase #7 $139.41   3.798%   $144.7048   $144.70   $144.70   $144.70  
  7 purchase totals = $834.92       $897.0925   $897.09   $897.10   $897.10