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 $107.69   6.496%   $114.6855   $114.69   $114.70   $114.70  
  Purchase #2 $190.96   8.351%   $206.9071   $206.91   $206.90   $206.90  
  Purchase #3 $27.71   4.699%   $29.0121   $29.01   $29.00   $29.00  
  Purchase #4 $153.64   9.870%   $168.8043   $168.80   $168.80   $168.80  
  Purchase #5 $96.66   12.732%   $108.9668   $108.97   $108.95   $109.00  
  Purchase #6 $119.66   10.801%   $132.5845   $132.58   $132.60   $132.60  
  Purchase #7 $156.93   4.269%   $163.6293   $163.63   $163.65   $163.60  
  7 purchase totals = $853.25       $924.5896   $924.59   $924.60   $924.60