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 $88.58   5.186%   $93.1738   $93.17   $93.15   $93.20  
  Purchase #2 $224.53   3.792%   $233.0442   $233.04   $233.05   $233.00  
  Purchase #3 $51.55   8.267%   $55.8116   $55.81   $55.80   $55.80  
  Purchase #4 $181.76   4.737%   $190.37   $190.37   $190.35   $190.40  
  Purchase #5 $238.45   11.416%   $265.6715   $265.67   $265.65   $265.70  
  Purchase #6 $42.60   11.412%   $47.4615   $47.46   $47.45   $47.50  
  Purchase #7 $14.27   4.569%   $14.922   $14.92   $14.90   $14.90  
  7 purchase totals = $841.74       $900.4546   $900.44   $900.35   $900.50