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 $55.35   13.775%   $62.9745   $62.97   $62.95   $63.00  
  Purchase #2 $16.48   12.554%   $18.5489   $18.55   $18.55   $18.50  
  Purchase #3 $44.25   5.618%   $46.736   $46.74   $46.75   $46.70  
  Purchase #4 $208.76   7.383%   $224.1728   $224.17   $224.15   $224.20  
  Purchase #5 $204.70   8.290%   $221.6696   $221.67   $221.65   $221.70  
  Purchase #6 $146.76   3.293%   $151.5928   $151.59   $151.60   $151.60  
  Purchase #7 $243.77   6.560%   $259.7613   $259.76   $259.75   $259.80  
  7 purchase totals = $920.07       $985.4559   $985.45   $985.40   $985.50