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 $74.97   13.712%   $85.2499   $85.25   $85.25   $85.20  
  Purchase #2 $50.36   7.506%   $54.14   $54.14   $54.15   $54.10  
  Purchase #3 $109.61   7.776%   $118.1333   $118.13   $118.15   $118.10  
  Purchase #4 $131.77   11.564%   $147.0079   $147.01   $147.00   $147.00  
  Purchase #5 $22.40   8.147%   $24.2249   $24.22   $24.20   $24.20  
  Purchase #6 $107.88   13.468%   $122.4093   $122.41   $122.40   $122.40  
  Purchase #7 $206.65   8.873%   $224.9861   $224.99   $225.00   $225.00  
  7 purchase totals = $703.64       $776.1514   $776.15   $776.15   $776.00