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 $140.90   11.156%   $156.6188   $156.62   $156.60   $156.60  
  Purchase #2 $219.91   3.224%   $226.9999   $227.00   $227.00   $227.00  
  Purchase #3 $164.58   4.453%   $171.9087   $171.91   $171.90   $171.90  
  Purchase #4 $124.72   10.235%   $137.4851   $137.49   $137.50   $137.50  
  Purchase #5 $158.56   8.446%   $171.952   $171.95   $171.95   $172.00  
  Purchase #6 $145.32   8.248%   $157.306   $157.31   $157.30   $157.30  
  Purchase #7 $137.92   4.421%   $144.0174   $144.02   $144.00   $144.00  
  7 purchase totals = $1,091.91       $1,166.2879   $1,166.30   $1,166.25   $1,166.30