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 $76.53   13.113%   $86.5654   $86.57   $86.55   $86.60  
  Purchase #2 $71.29   10.829%   $79.01   $79.01   $79.00   $79.00  
  Purchase #3 $114.68   4.391%   $119.7156   $119.72   $119.70   $119.70  
  Purchase #4 $164.74   10.693%   $182.3556   $182.36   $182.35   $182.40  
  Purchase #5 $177.41   4.768%   $185.8689   $185.87   $185.85   $185.90  
  Purchase #6 $110.30   10.328%   $121.6918   $121.69   $121.70   $121.70  
  Purchase #7 $163.66   10.761%   $181.2715   $181.27   $181.25   $181.30  
  7 purchase totals = $878.61       $956.4788   $956.49   $956.40   $956.60