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 $57.70   10.716%   $63.8831   $63.88   $63.90   $63.90  
  Purchase #2 $208.67   11.660%   $233.0009   $233.00   $233.00   $233.00  
  Purchase #3 $165.98   8.404%   $179.929   $179.93   $179.95   $179.90  
  Purchase #4 $185.42   13.807%   $211.0209   $211.02   $211.00   $211.00  
  Purchase #5 $144.90   11.595%   $161.7012   $161.70   $161.70   $161.70  
  Purchase #6 $178.45   9.302%   $195.0494   $195.05   $195.05   $195.00  
  Purchase #7 $21.57   13.537%   $24.4899   $24.49   $24.50   $24.50  
  7 purchase totals = $962.69       $1,069.0744   $1,069.07   $1,069.10   $1,069.00