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 $71.43   7.553%   $76.8251   $76.83   $76.85   $76.80  
  Purchase #2 $171.34   8.543%   $185.9776   $185.98   $186.00   $186.00  
  Purchase #3 $15.41   7.757%   $16.6054   $16.61   $16.60   $16.60  
  Purchase #4 $21.54   12.619%   $24.2581   $24.26   $24.25   $24.30  
  Purchase #5 $104.44   3.267%   $107.8521   $107.85   $107.85   $107.90  
  Purchase #6 $11.88   13.669%   $13.5039   $13.50   $13.50   $13.50  
  Purchase #7 $38.59   6.858%   $41.2365   $41.24   $41.25   $41.20  
  7 purchase totals = $434.63       $466.2587   $466.27   $466.30   $466.30