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 $88.95   6.203%   $94.4676   $94.47   $94.45   $94.50  
  Purchase #2 $116.67   9.385%   $127.6195   $127.62   $127.60   $127.60  
  Purchase #3 $249.65   5.630%   $263.7053   $263.71   $263.70   $263.70  
  Purchase #4 $41.38   9.395%   $45.2677   $45.27   $45.25   $45.30  
  Purchase #5 $106.81   7.360%   $114.6712   $114.67   $114.65   $114.70  
  Purchase #6 $75.26   7.204%   $80.6817   $80.68   $80.70   $80.70  
  Purchase #7 $17.64   4.659%   $18.4618   $18.46   $18.45   $18.50  
  7 purchase totals = $696.36       $744.8748   $744.88   $744.80   $745.00