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 $56.84   5.119%   $59.7496   $59.75   $59.75   $59.70  
  Purchase #2 $167.90   4.269%   $175.0677   $175.07   $175.05   $175.10  
  Purchase #3 $28.57   6.341%   $30.3816   $30.38   $30.40   $30.40  
  Purchase #4 $129.57   3.747%   $134.425   $134.43   $134.45   $134.40  
  Purchase #5 $6.85   7.849%   $7.3877   $7.39   $7.40   $7.40  
  Purchase #6 $137.71   13.315%   $156.0461   $156.05   $156.05   $156.00  
  Purchase #7 $203.98   4.507%   $213.1734   $213.17   $213.15   $213.20  
  7 purchase totals = $731.42       $776.2311   $776.24   $776.25   $776.20