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 $186.34   6.421%   $198.3049   $198.30   $198.30   $198.30  
  Purchase #2 $198.82   9.453%   $217.6145   $217.61   $217.60   $217.60  
  Purchase #3 $228.80   4.702%   $239.5582   $239.56   $239.55   $239.60  
  Purchase #4 $48.26   6.517%   $51.4051   $51.41   $51.40   $51.40  
  Purchase #5 $196.59   10.694%   $217.6133   $217.61   $217.60   $217.60  
  Purchase #6 $110.90   12.312%   $124.554   $124.55   $124.55   $124.60  
  Purchase #7 $76.62   6.856%   $81.8731   $81.87   $81.85   $81.90  
  7 purchase totals = $1,046.33       $1,130.9231   $1,130.91   $1,130.85   $1,131.00