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 $200.43   13.244%   $226.9749   $226.97   $226.95   $227.00  
  Purchase #2 $186.39   10.333%   $205.6497   $205.65   $205.65   $205.60  
  Purchase #3 $227.64   10.622%   $251.8199   $251.82   $251.80   $251.80  
  Purchase #4 $149.41   12.487%   $168.0668   $168.07   $168.05   $168.10  
  Purchase #5 $248.62   9.767%   $272.9027   $272.90   $272.90   $272.90  
  Purchase #6 $129.81   11.467%   $144.6953   $144.70   $144.70   $144.70  
  Purchase #7 $234.57   12.116%   $262.9905   $262.99   $263.00   $263.00  
  7 purchase totals = $1,376.87       $1,533.0998   $1,533.10   $1,533.05   $1,533.10