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 $60.63   10.430%   $66.9537   $66.95   $66.95   $67.00  
  Purchase #2 $90.81   8.599%   $98.6188   $98.62   $98.60   $98.60  
  Purchase #3 $7.63   12.746%   $8.6025   $8.60   $8.60   $8.60  
  Purchase #4 $179.98   7.788%   $193.9968   $194.00   $194.00   $194.00  
  Purchase #5 $157.86   12.693%   $177.8972   $177.90   $177.90   $177.90  
  Purchase #6 $169.35   3.778%   $175.748   $175.75   $175.75   $175.70  
  Purchase #7 $132.91   5.102%   $139.6911   $139.69   $139.70   $139.70  
  7 purchase totals = $799.17       $861.5081   $861.51   $861.50   $861.50