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 $194.33   12.177%   $217.9936   $217.99   $218.00   $218.00  
  Purchase #2 $24.46   8.534%   $26.5474   $26.55   $26.55   $26.50  
  Purchase #3 $68.35   4.278%   $71.274   $71.27   $71.25   $71.30  
  Purchase #4 $201.51   6.770%   $215.1522   $215.15   $215.15   $215.20  
  Purchase #5 $175.40   13.268%   $198.6721   $198.67   $198.65   $198.70  
  Purchase #6 $203.71   5.511%   $214.9365   $214.94   $214.95   $214.90  
  Purchase #7 $100.88   13.669%   $114.6693   $114.67   $114.65   $114.70  
  7 purchase totals = $968.64       $1,059.2451   $1,059.24   $1,059.20   $1,059.30