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 $23.49   10.866%   $26.0424   $26.04   $26.05   $26.00  
  Purchase #2 $55.35   8.385%   $59.9911   $59.99   $60.00   $60.00  
  Purchase #3 $154.94   5.430%   $163.3532   $163.35   $163.35   $163.40  
  Purchase #4 $165.48   11.434%   $184.401   $184.40   $184.40   $184.40  
  Purchase #5 $222.32   7.695%   $239.4275   $239.43   $239.45   $239.40  
  Purchase #6 $106.27   6.382%   $113.0522   $113.05   $113.05   $113.10  
  Purchase #7 $237.55   13.827%   $270.396   $270.40   $270.40   $270.40  
  7 purchase totals = $965.40       $1,056.6634   $1,056.66   $1,056.70   $1,056.70