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 $49.25   12.810%   $55.5589   $55.56   $55.55   $55.60  
  Purchase #2 $214.94   8.704%   $233.6484   $233.65   $233.65   $233.60  
  Purchase #3 $126.60   7.857%   $136.547   $136.55   $136.55   $136.50  
  Purchase #4 $56.38   5.500%   $59.4809   $59.48   $59.50   $59.50  
  Purchase #5 $202.39   3.361%   $209.1923   $209.19   $209.20   $209.20  
  Purchase #6 $188.65   5.534%   $199.0899   $199.09   $199.10   $199.10  
  Purchase #7 $24.25   8.668%   $26.352   $26.35   $26.35   $26.40  
  7 purchase totals = $862.46       $919.8694   $919.87   $919.90   $919.90