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 $96.72   6.299%   $102.8124   $102.81   $102.80   $102.80  
  Purchase #2 $248.86   4.682%   $260.5116   $260.51   $260.50   $260.50  
  Purchase #3 $124.48   6.454%   $132.5139   $132.51   $132.50   $132.50  
  Purchase #4 $190.25   4.153%   $198.1511   $198.15   $198.15   $198.20  
  Purchase #5 $45.57   12.432%   $51.2353   $51.24   $51.25   $51.20  
  Purchase #6 $175.39   5.325%   $184.7295   $184.73   $184.75   $184.70  
  Purchase #7 $108.34   5.326%   $114.1102   $114.11   $114.10   $114.10  
  7 purchase totals = $989.61       $1,044.0640   $1,044.06   $1,044.05   $1,044.00