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 $61.36   11.737%   $68.5618   $68.56   $68.55   $68.60  
  Purchase #2 $246.79   8.212%   $267.0564   $267.06   $267.05   $267.10  
  Purchase #3 $97.92   4.688%   $102.5105   $102.51   $102.50   $102.50  
  Purchase #4 $164.99   10.825%   $182.8502   $182.85   $182.85   $182.90  
  Purchase #5 $70.45   8.436%   $76.3932   $76.39   $76.40   $76.40  
  Purchase #6 $218.49   6.125%   $231.8725   $231.87   $231.85   $231.90  
  Purchase #7 $60.42   6.215%   $64.1751   $64.18   $64.20   $64.20  
  7 purchase totals = $920.42       $993.4197   $993.42   $993.40   $993.60