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 $92.55   5.467%   $97.6097   $97.61   $97.60   $97.60  
  Purchase #2 $41.72   13.243%   $47.245   $47.25   $47.25   $47.20  
  Purchase #3 $248.95   4.809%   $260.922   $260.92   $260.90   $260.90  
  Purchase #4 $208.67   3.154%   $215.2515   $215.25   $215.25   $215.30  
  Purchase #5 $85.63   13.463%   $97.1584   $97.16   $97.15   $97.20  
  Purchase #6 $38.74   4.823%   $40.6084   $40.61   $40.60   $40.60  
  Purchase #7 $49.89   5.165%   $52.4668   $52.47   $52.45   $52.50  
  7 purchase totals = $766.15       $811.2618   $811.27   $811.20   $811.30