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 $49.45   11.827%   $55.2985   $55.30   $55.30   $55.30  
  Purchase #2 $186.69   11.376%   $207.9279   $207.93   $207.95   $207.90  
  Purchase #3 $239.89   6.158%   $254.6624   $254.66   $254.65   $254.70  
  Purchase #4 $11.29   10.214%   $12.4432   $12.44   $12.45   $12.40  
  Purchase #5 $157.70   3.440%   $163.1249   $163.12   $163.10   $163.10  
  Purchase #6 $71.77   6.206%   $76.224   $76.22   $76.20   $76.20  
  Purchase #7 $241.75   12.468%   $271.8914   $271.89   $271.90   $271.90  
  7 purchase totals = $958.54       $1,041.5723   $1,041.56   $1,041.55   $1,041.50