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 $56.77   12.443%   $63.8339   $63.83   $63.85   $63.80  
  Purchase #2 $222.92   11.382%   $248.2928   $248.29   $248.30   $248.30  
  Purchase #3 $198.31   8.821%   $215.8029   $215.80   $215.80   $215.80  
  Purchase #4 $198.90   11.525%   $221.8232   $221.82   $221.80   $221.80  
  Purchase #5 $126.27   3.860%   $131.144   $131.14   $131.15   $131.10  
  Purchase #6 $113.60   8.739%   $123.5275   $123.53   $123.55   $123.50  
  Purchase #7 $179.68   12.197%   $201.5956   $201.60   $201.60   $201.60  
  7 purchase totals = $1,096.45       $1,206.0199   $1,206.01   $1,206.05   $1,205.90