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 $217.39   3.331%   $224.6313   $224.63   $224.65   $224.60  
  Purchase #2 $38.96   8.723%   $42.3585   $42.36   $42.35   $42.40  
  Purchase #3 $181.43   11.486%   $202.269   $202.27   $202.25   $202.30  
  Purchase #4 $124.73   11.678%   $139.296   $139.30   $139.30   $139.30  
  Purchase #5 $242.91   4.536%   $253.9284   $253.93   $253.95   $253.90  
  Purchase #6 $94.43   10.292%   $104.1487   $104.15   $104.15   $104.10  
  Purchase #7 $69.47   9.699%   $76.2079   $76.21   $76.20   $76.20  
  7 purchase totals = $969.32       $1,042.8398   $1,042.85   $1,042.85   $1,042.80