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 $40.95   12.682%   $46.1433   $46.14   $46.15   $46.10  
  Purchase #2 $18.54   3.683%   $19.2228   $19.22   $19.20   $19.20  
  Purchase #3 $91.54   5.468%   $96.5454   $96.55   $96.55   $96.50  
  Purchase #4 $76.34   11.481%   $85.1046   $85.10   $85.10   $85.10  
  Purchase #5 $247.77   8.616%   $269.1179   $269.12   $269.10   $269.10  
  Purchase #6 $237.57   5.226%   $249.9854   $249.99   $250.00   $250.00  
  Purchase #7 $217.36   8.685%   $236.2377   $236.24   $236.25   $236.20  
  7 purchase totals = $930.07       $1,002.3571   $1,002.36   $1,002.35   $1,002.20