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 $247.90   8.480%   $268.9219   $268.92   $268.90   $268.90  
  Purchase #2 $77.83   7.121%   $83.3723   $83.37   $83.35   $83.40  
  Purchase #3 $66.63   12.693%   $75.0873   $75.09   $75.10   $75.10  
  Purchase #4 $249.66   4.471%   $260.8223   $260.82   $260.80   $260.80  
  Purchase #5 $41.84   11.473%   $46.6403   $46.64   $46.65   $46.60  
  Purchase #6 $129.48   5.371%   $136.4344   $136.43   $136.45   $136.40  
  Purchase #7 $175.41   8.859%   $190.9496   $190.95   $190.95   $190.90  
  7 purchase totals = $988.75       $1,062.2281   $1,062.22   $1,062.20   $1,062.10