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 $47.96   6.499%   $51.0769   $51.08   $51.10   $51.10  
  Purchase #2 $114.62   6.828%   $122.4463   $122.45   $122.45   $122.40  
  Purchase #3 $67.28   4.871%   $70.5572   $70.56   $70.55   $70.60  
  Purchase #4 $185.40   3.845%   $192.5286   $192.53   $192.55   $192.50  
  Purchase #5 $91.25   13.232%   $103.3242   $103.32   $103.30   $103.30  
  Purchase #6 $172.34   5.686%   $182.1393   $182.14   $182.15   $182.10  
  Purchase #7 $119.33   12.671%   $134.4503   $134.45   $134.45   $134.50  
  7 purchase totals = $798.18       $856.5228   $856.53   $856.55   $856.50