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 $68.66   10.198%   $75.6619   $75.66   $75.65   $75.70  
  Purchase #2 $30.25   10.572%   $33.448   $33.45   $33.45   $33.40  
  Purchase #3 $245.69   5.518%   $259.2472   $259.25   $259.25   $259.20  
  Purchase #4 $214.51   6.838%   $229.1782   $229.18   $229.20   $229.20  
  Purchase #5 $237.64   13.297%   $269.239   $269.24   $269.25   $269.20  
  Purchase #6 $13.83   9.564%   $15.1527   $15.15   $15.15   $15.20  
  Purchase #7 $71.44   6.755%   $76.2658   $76.27   $76.25   $76.30  
  7 purchase totals = $882.02       $958.1928   $958.20   $958.20   $958.20