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 $81.46   5.577%   $86.003   $86.00   $86.00   $86.00  
  Purchase #2 $230.72   7.814%   $248.7485   $248.75   $248.75   $248.70  
  Purchase #3 $55.66   3.388%   $57.5458   $57.55   $57.55   $57.50  
  Purchase #4 $118.97   8.805%   $129.4453   $129.45   $129.45   $129.40  
  Purchase #5 $98.27   11.259%   $109.3342   $109.33   $109.35   $109.30  
  Purchase #6 $248.71   10.206%   $274.0933   $274.09   $274.10   $274.10  
  Purchase #7 $91.92   3.387%   $95.0333   $95.03   $95.05   $95.00  
  7 purchase totals = $925.71       $1,000.2034   $1,000.20   $1,000.25   $1,000.00