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 $64.88   6.736%   $69.2503   $69.25   $69.25   $69.30  
  Purchase #2 $27.64   11.158%   $30.7241   $30.72   $30.70   $30.70  
  Purchase #3 $79.87   6.364%   $84.9529   $84.95   $84.95   $85.00  
  Purchase #4 $64.80   10.398%   $71.5379   $71.54   $71.55   $71.50  
  Purchase #5 $103.46   6.392%   $110.0732   $110.07   $110.05   $110.10  
  Purchase #6 $248.44   13.872%   $282.9036   $282.90   $282.90   $282.90  
  Purchase #7 $104.84   7.759%   $112.9745   $112.97   $112.95   $113.00  
  7 purchase totals = $693.93       $762.4165   $762.40   $762.35   $762.50