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 $56.45   6.447%   $60.0893   $60.09   $60.10   $60.10  
  Purchase #2 $131.68   5.559%   $139.0001   $139.00   $139.00   $139.00  
  Purchase #3 $219.99   10.293%   $242.6336   $242.63   $242.65   $242.60  
  Purchase #4 $238.93   12.444%   $268.6624   $268.66   $268.65   $268.70  
  Purchase #5 $35.69   4.426%   $37.2696   $37.27   $37.25   $37.30  
  Purchase #6 $146.27   9.713%   $160.4772   $160.48   $160.50   $160.50  
  Purchase #7 $53.28   8.771%   $57.9532   $57.95   $57.95   $58.00  
  7 purchase totals = $882.29       $966.0854   $966.08   $966.10   $966.20