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 $239.80   11.278%   $266.8446   $266.84   $266.85   $266.80  
  Purchase #2 $188.81   10.460%   $208.5595   $208.56   $208.55   $208.60  
  Purchase #3 $206.92   10.346%   $228.3279   $228.33   $228.35   $228.30  
  Purchase #4 $94.36   11.556%   $105.2642   $105.26   $105.25   $105.30  
  Purchase #5 $39.30   6.395%   $41.8132   $41.81   $41.80   $41.80  
  Purchase #6 $227.73   11.463%   $253.8347   $253.83   $253.85   $253.80  
  Purchase #7 $19.99   11.549%   $22.2986   $22.30   $22.30   $22.30  
  7 purchase totals = $1,016.91       $1,126.9427   $1,126.93   $1,126.95   $1,126.90