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 $56.66   12.535%   $63.7623   $63.76   $63.75   $63.80  
  Purchase #2 $231.62   5.595%   $244.5791   $244.58   $244.60   $244.60  
  Purchase #3 $7.57   10.523%   $8.3666   $8.37   $8.35   $8.40  
  Purchase #4 $248.29   8.694%   $269.8763   $269.88   $269.90   $269.90  
  Purchase #5 $215.44   6.306%   $229.0256   $229.03   $229.05   $229.00  
  Purchase #6 $176.75   6.520%   $188.2741   $188.27   $188.25   $188.30  
  Purchase #7 $208.60   6.705%   $222.5866   $222.59   $222.60   $222.60  
  7 purchase totals = $1,144.93       $1,226.4706   $1,226.48   $1,226.50   $1,226.60