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 $182.65   13.292%   $206.9278   $206.93   $206.95   $206.90  
  Purchase #2 $78.51   11.692%   $87.6894   $87.69   $87.70   $87.70  
  Purchase #3 $96.83   12.727%   $109.1536   $109.15   $109.15   $109.20  
  Purchase #4 $238.69   8.293%   $258.4846   $258.48   $258.50   $258.50  
  Purchase #5 $30.81   3.469%   $31.8788   $31.88   $31.90   $31.90  
  Purchase #6 $25.65   4.694%   $26.854   $26.85   $26.85   $26.90  
  Purchase #7 $67.40   11.808%   $75.3586   $75.36   $75.35   $75.40  
  7 purchase totals = $720.54       $796.3468   $796.34   $796.40   $796.50