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 $64.87   6.462%   $69.0619   $69.06   $69.05   $69.10  
  Purchase #2 $19.58   5.711%   $20.6982   $20.70   $20.70   $20.70  
  Purchase #3 $49.90   4.164%   $51.9778   $51.98   $52.00   $52.00  
  Purchase #4 $247.74   6.380%   $263.5458   $263.55   $263.55   $263.50  
  Purchase #5 $178.50   8.557%   $193.7742   $193.77   $193.75   $193.80  
  Purchase #6 $185.77   6.720%   $198.2537   $198.25   $198.25   $198.30  
  Purchase #7 $75.80   12.514%   $85.2856   $85.29   $85.30   $85.30  
  7 purchase totals = $822.16       $882.5972   $882.60   $882.60   $882.70