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 $89.42   3.425%   $92.4826   $92.48   $92.50   $92.50  
  Purchase #2 $110.45   13.748%   $125.6347   $125.63   $125.65   $125.60  
  Purchase #3 $164.34   3.724%   $170.46   $170.46   $170.45   $170.50  
  Purchase #4 $166.32   8.401%   $180.2925   $180.29   $180.30   $180.30  
  Purchase #5 $193.44   6.839%   $206.6694   $206.67   $206.65   $206.70  
  Purchase #6 $200.55   10.671%   $221.9507   $221.95   $221.95   $222.00  
  Purchase #7 $58.48   4.587%   $61.1625   $61.16   $61.15   $61.20  
  7 purchase totals = $983.00       $1,058.6524   $1,058.64   $1,058.65   $1,058.80