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 $55.93   13.705%   $63.5952   $63.60   $63.60   $63.60  
  Purchase #2 $139.85   13.339%   $158.5046   $158.50   $158.50   $158.50  
  Purchase #3 $43.26   11.583%   $48.2708   $48.27   $48.25   $48.30  
  Purchase #4 $214.91   6.450%   $228.7717   $228.77   $228.75   $228.80  
  Purchase #5 $56.79   10.811%   $62.9296   $62.93   $62.95   $62.90  
  Purchase #6 $124.50   5.429%   $131.2591   $131.26   $131.25   $131.30  
  Purchase #7 $41.44   12.360%   $46.562   $46.56   $46.55   $46.60  
  7 purchase totals = $676.68       $739.8930   $739.89   $739.85   $740.00