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 $203.85   7.802%   $219.7544   $219.75   $219.75   $219.80  
  Purchase #2 $59.57   13.419%   $67.5637   $67.56   $67.55   $67.60  
  Purchase #3 $120.72   3.472%   $124.9114   $124.91   $124.90   $124.90  
  Purchase #4 $214.54   5.451%   $226.2346   $226.23   $226.25   $226.20  
  Purchase #5 $8.83   11.858%   $9.8771   $9.88   $9.90   $9.90  
  Purchase #6 $123.27   8.105%   $133.261   $133.26   $133.25   $133.30  
  Purchase #7 $164.84   10.780%   $182.6098   $182.61   $182.60   $182.60  
  7 purchase totals = $895.62       $964.2120   $964.20   $964.20   $964.30