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 $197.42   3.871%   $205.0621   $205.06   $205.05   $205.10  
  Purchase #2 $226.97   6.517%   $241.7616   $241.76   $241.75   $241.80  
  Purchase #3 $38.96   11.383%   $43.3948   $43.39   $43.40   $43.40  
  Purchase #4 $54.93   13.872%   $62.5499   $62.55   $62.55   $62.50  
  Purchase #5 $47.96   12.697%   $54.0495   $54.05   $54.05   $54.00  
  Purchase #6 $112.27   8.394%   $121.6939   $121.69   $121.70   $121.70  
  Purchase #7 $191.38   8.368%   $207.3947   $207.39   $207.40   $207.40  
  7 purchase totals = $869.89       $935.9065   $935.89   $935.90   $935.90