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 $183.94   12.430%   $206.8037   $206.80   $206.80   $206.80  
  Purchase #2 $40.85   7.557%   $43.937   $43.94   $43.95   $43.90  
  Purchase #3 $26.69   3.154%   $27.5318   $27.53   $27.55   $27.50  
  Purchase #4 $214.36   3.871%   $222.6579   $222.66   $222.65   $222.70  
  Purchase #5 $98.37   11.529%   $109.7111   $109.71   $109.70   $109.70  
  Purchase #6 $144.50   4.598%   $151.1441   $151.14   $151.15   $151.10  
  Purchase #7 $5.28   12.235%   $5.926   $5.93   $5.95   $5.90  
  7 purchase totals = $713.99       $767.7116   $767.71   $767.75   $767.60