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 $239.98   3.702%   $248.8641   $248.86   $248.85   $248.90  
  Purchase #2 $70.40   9.187%   $76.8676   $76.87   $76.85   $76.90  
  Purchase #3 $100.51   13.419%   $113.9974   $114.00   $114.00   $114.00  
  Purchase #4 $49.28   10.845%   $54.6244   $54.62   $54.60   $54.60  
  Purchase #5 $67.88   13.497%   $77.0418   $77.04   $77.05   $77.00  
  Purchase #6 $63.36   3.442%   $65.5409   $65.54   $65.55   $65.50  
  Purchase #7 $58.68   10.698%   $64.9576   $64.96   $64.95   $65.00  
  7 purchase totals = $650.09       $701.8938   $701.89   $701.85   $701.90