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 $55.98   8.402%   $60.6834   $60.68   $60.70   $60.70  
  Purchase #2 $177.58   5.168%   $186.7573   $186.76   $186.75   $186.80  
  Purchase #3 $229.45   8.641%   $249.2768   $249.28   $249.30   $249.30  
  Purchase #4 $225.77   6.201%   $239.77   $239.77   $239.75   $239.80  
  Purchase #5 $35.65   7.605%   $38.3612   $38.36   $38.35   $38.40  
  Purchase #6 $54.55   12.210%   $61.2106   $61.21   $61.20   $61.20  
  Purchase #7 $114.34   8.359%   $123.8977   $123.90   $123.90   $123.90  
  7 purchase totals = $893.32       $959.9570   $959.96   $959.95   $960.10