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 $61.83   10.121%   $68.0878   $68.09   $68.10   $68.10  
  Purchase #2 $25.38   11.626%   $28.3307   $28.33   $28.35   $28.30  
  Purchase #3 $90.46   8.724%   $98.3517   $98.35   $98.35   $98.40  
  Purchase #4 $61.92   9.227%   $67.6334   $67.63   $67.65   $67.60  
  Purchase #5 $213.68   7.681%   $230.0928   $230.09   $230.10   $230.10  
  Purchase #6 $68.94   10.251%   $76.007   $76.01   $76.00   $76.00  
  Purchase #7 $127.61   10.564%   $141.0907   $141.09   $141.10   $141.10  
  7 purchase totals = $649.82       $709.5941   $709.59   $709.65   $709.60