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 $210.39   6.861%   $224.8249   $224.82   $224.80   $224.80  
  Purchase #2 $93.83   3.852%   $97.4443   $97.44   $97.45   $97.40  
  Purchase #3 $129.74   8.535%   $140.8133   $140.81   $140.80   $140.80  
  Purchase #4 $95.75   13.252%   $108.4388   $108.44   $108.45   $108.40  
  Purchase #5 $167.62   5.745%   $177.2498   $177.25   $177.25   $177.20  
  Purchase #6 $159.70   6.794%   $170.55   $170.55   $170.55   $170.60  
  Purchase #7 $67.91   12.664%   $76.5101   $76.51   $76.50   $76.50  
  7 purchase totals = $924.94       $995.8312   $995.82   $995.80   $995.70