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 $181.99   7.823%   $196.2271   $196.23   $196.25   $196.20  
  Purchase #2 $232.57   11.347%   $258.9597   $258.96   $258.95   $259.00  
  Purchase #3 $37.99   9.699%   $41.6747   $41.67   $41.65   $41.70  
  Purchase #4 $97.68   10.712%   $108.1435   $108.14   $108.15   $108.10  
  Purchase #5 $228.38   10.480%   $252.3142   $252.31   $252.30   $252.30  
  Purchase #6 $51.83   12.735%   $58.4306   $58.43   $58.45   $58.40  
  Purchase #7 $62.95   11.693%   $70.3107   $70.31   $70.30   $70.30  
  7 purchase totals = $893.39       $986.0605   $986.05   $986.05   $986.00