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 $214.33   11.768%   $239.5524   $239.55   $239.55   $239.60  
  Purchase #2 $202.39   7.183%   $216.9277   $216.93   $216.95   $216.90  
  Purchase #3 $163.54   10.208%   $180.2342   $180.23   $180.25   $180.20  
  Purchase #4 $118.84   4.216%   $123.8503   $123.85   $123.85   $123.90  
  Purchase #5 $208.25   11.290%   $231.7614   $231.76   $231.75   $231.80  
  Purchase #6 $76.46   5.650%   $80.78   $80.78   $80.80   $80.80  
  Purchase #7 $237.93   10.783%   $263.586   $263.59   $263.60   $263.60  
  7 purchase totals = $1,221.74       $1,336.6920   $1,336.69   $1,336.75   $1,336.80