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 $85.42   13.244%   $96.733   $96.73   $96.75   $96.70  
  Purchase #2 $199.38   13.707%   $226.709   $226.71   $226.70   $226.70  
  Purchase #3 $44.84   10.729%   $49.6509   $49.65   $49.65   $49.70  
  Purchase #4 $239.91   3.698%   $248.7819   $248.78   $248.80   $248.80  
  Purchase #5 $65.49   12.511%   $73.6835   $73.68   $73.70   $73.70  
  Purchase #6 $237.45   10.106%   $261.4467   $261.45   $261.45   $261.40  
  Purchase #7 $97.34   10.298%   $107.3641   $107.36   $107.35   $107.40  
  7 purchase totals = $969.83       $1,064.3691   $1,064.36   $1,064.40   $1,064.40