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 $24.61   5.796%   $26.0364   $26.04   $26.05   $26.00  
  Purchase #2 $48.31   10.193%   $53.2342   $53.23   $53.25   $53.20  
  Purchase #3 $181.60   11.273%   $202.0718   $202.07   $202.05   $202.10  
  Purchase #4 $129.47   5.379%   $136.4342   $136.43   $136.45   $136.40  
  Purchase #5 $201.25   3.193%   $207.6759   $207.68   $207.70   $207.70  
  Purchase #6 $200.75   8.442%   $217.6973   $217.70   $217.70   $217.70  
  Purchase #7 $136.84   6.161%   $145.2707   $145.27   $145.25   $145.30  
  7 purchase totals = $922.83       $988.4205   $988.42   $988.45   $988.40