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 $226.55   12.824%   $255.6028   $255.60   $255.60   $255.60  
  Purchase #2 $236.92   10.387%   $261.5289   $261.53   $261.55   $261.50  
  Purchase #3 $10.90   6.183%   $11.5739   $11.57   $11.55   $11.60  
  Purchase #4 $114.94   13.715%   $130.704   $130.70   $130.70   $130.70  
  Purchase #5 $211.90   7.187%   $227.1293   $227.13   $227.15   $227.10  
  Purchase #6 $94.26   3.439%   $97.5016   $97.50   $97.50   $97.50  
  Purchase #7 $70.41   13.412%   $79.8534   $79.85   $79.85   $79.90  
  7 purchase totals = $965.88       $1,063.8939   $1,063.88   $1,063.90   $1,063.90