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 $67.95   12.413%   $76.3846   $76.38   $76.40   $76.40  
  Purchase #2 $63.84   8.112%   $69.0187   $69.02   $69.00   $69.00  
  Purchase #3 $116.40   12.566%   $131.0268   $131.03   $131.05   $131.00  
  Purchase #4 $156.26   4.689%   $163.587   $163.59   $163.60   $163.60  
  Purchase #5 $46.80   5.482%   $49.3656   $49.37   $49.35   $49.40  
  Purchase #6 $139.59   9.468%   $152.8064   $152.81   $152.80   $152.80  
  Purchase #7 $179.84   5.798%   $190.2671   $190.27   $190.25   $190.30  
  7 purchase totals = $770.68       $832.4562   $832.47   $832.45   $832.50