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 $109.34   4.559%   $114.3248   $114.32   $114.30   $114.30  
  Purchase #2 $184.99   4.669%   $193.6272   $193.63   $193.65   $193.60  
  Purchase #3 $234.29   13.144%   $265.0851   $265.09   $265.10   $265.10  
  Purchase #4 $26.39   3.713%   $27.3699   $27.37   $27.35   $27.40  
  Purchase #5 $67.27   7.203%   $72.1155   $72.12   $72.10   $72.10  
  Purchase #6 $34.41   8.115%   $37.2024   $37.20   $37.20   $37.20  
  Purchase #7 $68.83   9.397%   $75.298   $75.30   $75.30   $75.30  
  7 purchase totals = $725.52       $785.0229   $785.03   $785.00   $785.00