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 $58.33   8.853%   $63.494   $63.49   $63.50   $63.50  
  Purchase #2 $120.81   7.203%   $129.5119   $129.51   $129.50   $129.50  
  Purchase #3 $33.63   4.412%   $35.1138   $35.11   $35.10   $35.10  
  Purchase #4 $20.71   12.823%   $23.3656   $23.37   $23.35   $23.40  
  Purchase #5 $235.76   5.364%   $248.4062   $248.41   $248.40   $248.40  
  Purchase #6 $116.90   6.553%   $124.5605   $124.56   $124.55   $124.60  
  Purchase #7 $197.54   8.410%   $214.1531   $214.15   $214.15   $214.20  
  7 purchase totals = $783.68       $838.6051   $838.60   $838.55   $838.70