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 $55.82   13.831%   $63.5405   $63.54   $63.55   $63.50  
  Purchase #2 $113.41   3.433%   $117.3034   $117.30   $117.30   $117.30  
  Purchase #3 $67.67   11.704%   $75.5901   $75.59   $75.60   $75.60  
  Purchase #4 $140.81   9.390%   $154.0321   $154.03   $154.05   $154.00  
  Purchase #5 $163.81   8.396%   $177.5635   $177.56   $177.55   $177.60  
  Purchase #6 $161.54   11.187%   $179.6115   $179.61   $179.60   $179.60  
  Purchase #7 $218.60   11.630%   $244.0232   $244.02   $244.00   $244.00  
  7 purchase totals = $921.66       $1,011.6643   $1,011.65   $1,011.65   $1,011.60