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 $66.66   13.415%   $75.6024   $75.60   $75.60   $75.60  
  Purchase #2 $192.57   12.128%   $215.9249   $215.92   $215.90   $215.90  
  Purchase #3 $12.54   12.479%   $14.1049   $14.10   $14.10   $14.10  
  Purchase #4 $89.72   5.106%   $94.3011   $94.30   $94.30   $94.30  
  Purchase #5 $73.98   13.420%   $83.9081   $83.91   $83.90   $83.90  
  Purchase #6 $79.82   4.853%   $83.6937   $83.69   $83.70   $83.70  
  Purchase #7 $102.48   11.797%   $114.5696   $114.57   $114.55   $114.60  
  7 purchase totals = $617.77       $682.1047   $682.09   $682.05   $682.10