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 $190.95   6.157%   $202.7068   $202.71   $202.70   $202.70  
  Purchase #2 $51.92   13.379%   $58.8664   $58.87   $58.85   $58.90  
  Purchase #3 $35.72   13.727%   $40.6233   $40.62   $40.60   $40.60  
  Purchase #4 $193.43   11.354%   $215.392   $215.39   $215.40   $215.40  
  Purchase #5 $37.80   7.660%   $40.6955   $40.70   $40.70   $40.70  
  Purchase #6 $5.38   4.312%   $5.612   $5.61   $5.60   $5.60  
  Purchase #7 $58.64   12.555%   $66.0023   $66.00   $66.00   $66.00  
  7 purchase totals = $573.84       $629.8983   $629.90   $629.85   $629.90