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 $61.62   13.123%   $69.7064   $69.71   $69.70   $69.70  
  Purchase #2 $68.48   4.726%   $71.7164   $71.72   $71.70   $71.70  
  Purchase #3 $221.93   6.544%   $236.4531   $236.45   $236.45   $236.50  
  Purchase #4 $49.57   11.373%   $55.2076   $55.21   $55.20   $55.20  
  Purchase #5 $199.58   8.703%   $216.9494   $216.95   $216.95   $216.90  
  Purchase #6 $32.78   4.564%   $34.2761   $34.28   $34.30   $34.30  
  Purchase #7 $183.73   10.695%   $203.3799   $203.38   $203.40   $203.40  
  7 purchase totals = $817.69       $887.6889   $887.70   $887.70   $887.70