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 $238.56   12.507%   $268.3967   $268.40   $268.40   $268.40  
  Purchase #2 $199.30   9.211%   $217.6575   $217.66   $217.65   $217.70  
  Purchase #3 $107.37   6.787%   $114.6572   $114.66   $114.65   $114.70  
  Purchase #4 $84.30   4.468%   $88.0665   $88.07   $88.05   $88.10  
  Purchase #5 $44.89   4.678%   $46.99   $46.99   $47.00   $47.00  
  Purchase #6 $207.81   13.710%   $236.3008   $236.30   $236.30   $236.30  
  Purchase #7 $174.34   4.687%   $182.5113   $182.51   $182.50   $182.50  
  7 purchase totals = $1,056.57       $1,154.5800   $1,154.59   $1,154.55   $1,154.70