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 $219.96   10.318%   $242.6555   $242.66   $242.65   $242.70  
  Purchase #2 $175.72   3.600%   $182.0459   $182.05   $182.05   $182.00  
  Purchase #3 $19.80   9.722%   $21.725   $21.73   $21.75   $21.70  
  Purchase #4 $127.28   7.505%   $136.8324   $136.83   $136.85   $136.80  
  Purchase #5 $135.29   13.602%   $153.6921   $153.69   $153.70   $153.70  
  Purchase #6 $221.40   5.733%   $234.0929   $234.09   $234.10   $234.10  
  Purchase #7 $22.71   8.843%   $24.7182   $24.72   $24.70   $24.70  
  7 purchase totals = $922.16       $995.7620   $995.77   $995.80   $995.70