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 $92.87   10.484%   $102.6065   $102.61   $102.60   $102.60  
  Purchase #2 $226.43   11.312%   $252.0438   $252.04   $252.05   $252.00  
  Purchase #3 $23.91   12.447%   $26.8861   $26.89   $26.90   $26.90  
  Purchase #4 $5.60   10.779%   $6.2036   $6.20   $6.20   $6.20  
  Purchase #5 $169.32   11.180%   $188.25   $188.25   $188.25   $188.30  
  Purchase #6 $244.54   3.715%   $253.6247   $253.62   $253.60   $253.60  
  Purchase #7 $139.82   5.770%   $147.8876   $147.89   $147.90   $147.90  
  7 purchase totals = $902.49       $977.5023   $977.50   $977.50   $977.50