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 $75.88   11.687%   $84.7481   $84.75   $84.75   $84.70  
  Purchase #2 $139.97   4.432%   $146.1735   $146.17   $146.15   $146.20  
  Purchase #3 $184.89   8.522%   $200.6463   $200.65   $200.65   $200.60  
  Purchase #4 $8.78   5.709%   $9.2813   $9.28   $9.30   $9.30  
  Purchase #5 $19.67   11.859%   $22.0027   $22.00   $22.00   $22.00  
  Purchase #6 $231.62   11.734%   $258.7983   $258.80   $258.80   $258.80  
  Purchase #7 $164.25   13.702%   $186.7555   $186.76   $186.75   $186.80  
  7 purchase totals = $825.06       $908.4057   $908.41   $908.40   $908.40