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 $60.83   3.719%   $63.0923   $63.09   $63.10   $63.10  
  Purchase #2 $189.55   9.705%   $207.9458   $207.95   $207.95   $207.90  
  Purchase #3 $135.62   7.778%   $146.1685   $146.17   $146.15   $146.20  
  Purchase #4 $78.40   4.578%   $81.9892   $81.99   $82.00   $82.00  
  Purchase #5 $81.76   8.332%   $88.5722   $88.57   $88.55   $88.60  
  Purchase #6 $184.45   11.538%   $205.7318   $205.73   $205.75   $205.70  
  Purchase #7 $154.38   8.150%   $166.962   $166.96   $166.95   $167.00  
  7 purchase totals = $884.99       $960.4618   $960.46   $960.45   $960.50