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 $240.50   10.293%   $265.2547   $265.25   $265.25   $265.30  
  Purchase #2 $47.62   12.456%   $53.5515   $53.55   $53.55   $53.60  
  Purchase #3 $204.63   11.255%   $227.6611   $227.66   $227.65   $227.70  
  Purchase #4 $98.80   8.296%   $106.9964   $107.00   $107.00   $107.00  
  Purchase #5 $44.32   9.394%   $48.4834   $48.48   $48.50   $48.50  
  Purchase #6 $154.86   12.727%   $174.569   $174.57   $174.55   $174.60  
  Purchase #7 $119.83   13.239%   $135.6943   $135.69   $135.70   $135.70  
  7 purchase totals = $910.56       $1,012.2104   $1,012.20   $1,012.20   $1,012.40