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 $58.69   13.443%   $66.5797   $66.58   $66.60   $66.60  
  Purchase #2 $86.26   8.415%   $93.5188   $93.52   $93.50   $93.50  
  Purchase #3 $38.59   8.723%   $41.9562   $41.96   $41.95   $42.00  
  Purchase #4 $104.53   9.756%   $114.7279   $114.73   $114.75   $114.70  
  Purchase #5 $205.55   10.318%   $226.7586   $226.76   $226.75   $226.80  
  Purchase #6 $218.74   3.601%   $226.6168   $226.62   $226.60   $226.60  
  Purchase #7 $185.32   9.151%   $202.2786   $202.28   $202.30   $202.30  
  7 purchase totals = $897.68       $972.4366   $972.45   $972.45   $972.50