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 $226.91   5.169%   $238.639   $238.64   $238.65   $238.60  
  Purchase #2 $240.58   10.543%   $265.9443   $265.94   $265.95   $265.90  
  Purchase #3 $158.72   11.862%   $177.5474   $177.55   $177.55   $177.50  
  Purchase #4 $246.80   6.438%   $262.689   $262.69   $262.70   $262.70  
  Purchase #5 $95.72   3.226%   $98.8079   $98.81   $98.80   $98.80  
  Purchase #6 $231.89   6.555%   $247.0904   $247.09   $247.10   $247.10  
  Purchase #7 $155.85   4.672%   $163.1313   $163.13   $163.15   $163.10  
  7 purchase totals = $1,356.47       $1,453.8493   $1,453.85   $1,453.90   $1,453.70