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 $65.68   11.254%   $73.0716   $73.07   $73.05   $73.10  
  Purchase #2 $167.93   9.482%   $183.8531   $183.85   $183.85   $183.90  
  Purchase #3 $224.40   13.208%   $254.0388   $254.04   $254.05   $254.00  
  Purchase #4 $110.70   3.162%   $114.2003   $114.20   $114.20   $114.20  
  Purchase #5 $93.68   13.397%   $106.2303   $106.23   $106.25   $106.20  
  Purchase #6 $59.88   4.685%   $62.6854   $62.69   $62.70   $62.70  
  Purchase #7 $14.40   6.552%   $15.3435   $15.34   $15.35   $15.30  
  7 purchase totals = $736.67       $809.4230   $809.42   $809.45   $809.40