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 $188.89   11.711%   $211.0109   $211.01   $211.00   $211.00  
  Purchase #2 $131.54   8.702%   $142.9866   $142.99   $143.00   $143.00  
  Purchase #3 $32.31   11.343%   $35.9749   $35.97   $35.95   $36.00  
  Purchase #4 $248.91   7.159%   $266.7295   $266.73   $266.75   $266.70  
  Purchase #5 $184.81   6.559%   $196.9317   $196.93   $196.95   $196.90  
  Purchase #6 $171.52   12.207%   $192.4574   $192.46   $192.45   $192.50  
  Purchase #7 $213.71   13.416%   $242.3813   $242.38   $242.40   $242.40  
  7 purchase totals = $1,171.69       $1,288.4723   $1,288.47   $1,288.50   $1,288.50