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 $49.44   13.819%   $56.2721   $56.27   $56.25   $56.30  
  Purchase #2 $107.98   4.353%   $112.6804   $112.68   $112.70   $112.70  
  Purchase #3 $33.32   7.246%   $35.7344   $35.73   $35.75   $35.70  
  Purchase #4 $219.99   12.342%   $247.1412   $247.14   $247.15   $247.10  
  Purchase #5 $85.53   13.641%   $97.1971   $97.20   $97.20   $97.20  
  Purchase #6 $161.85   12.605%   $182.2512   $182.25   $182.25   $182.30  
  Purchase #7 $96.29   6.483%   $102.5325   $102.53   $102.55   $102.50  
  7 purchase totals = $754.40       $833.8089   $833.80   $833.85   $833.80