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 $103.53   9.743%   $113.6169   $113.62   $113.60   $113.60  
  Purchase #2 $99.83   12.161%   $111.9703   $111.97   $111.95   $112.00  
  Purchase #3 $31.48   4.823%   $32.9983   $33.00   $33.00   $33.00  
  Purchase #4 $61.41   3.595%   $63.6177   $63.62   $63.60   $63.60  
  Purchase #5 $89.30   9.600%   $97.8728   $97.87   $97.85   $97.90  
  Purchase #6 $248.69   9.455%   $272.2036   $272.20   $272.20   $272.20  
  Purchase #7 $72.80   11.628%   $81.2652   $81.27   $81.25   $81.30  
  7 purchase totals = $707.04       $773.5448   $773.55   $773.45   $773.60