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 $54.60   12.737%   $61.5544   $61.55   $61.55   $61.60  
  Purchase #2 $96.65   4.574%   $101.0708   $101.07   $101.05   $101.10  
  Purchase #3 $188.91   6.802%   $201.7597   $201.76   $201.75   $201.80  
  Purchase #4 $40.35   6.691%   $43.0498   $43.05   $43.05   $43.00  
  Purchase #5 $50.94   13.354%   $57.7425   $57.74   $57.75   $57.70  
  Purchase #6 $248.47   5.802%   $262.8862   $262.89   $262.90   $262.90  
  Purchase #7 $163.56   6.552%   $174.2765   $174.28   $174.30   $174.30  
  7 purchase totals = $843.48       $902.3399   $902.34   $902.35   $902.40