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 $61.36   10.280%   $67.6678   $67.67   $67.65   $67.70  
  Purchase #2 $180.49   5.620%   $190.6335   $190.63   $190.65   $190.60  
  Purchase #3 $248.78   4.127%   $259.0472   $259.05   $259.05   $259.00  
  Purchase #4 $156.30   13.239%   $176.9926   $176.99   $177.00   $177.00  
  Purchase #5 $102.46   11.622%   $114.3679   $114.37   $114.35   $114.40  
  Purchase #6 $25.28   8.781%   $27.4998   $27.50   $27.50   $27.50  
  Purchase #7 $154.60   4.795%   $162.0131   $162.01   $162.00   $162.00  
  7 purchase totals = $929.27       $998.2219   $998.22   $998.20   $998.20