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 $236.95   9.617%   $259.7375   $259.74   $259.75   $259.70  
  Purchase #2 $179.88   4.436%   $187.8595   $187.86   $187.85   $187.90  
  Purchase #3 $163.74   3.864%   $170.0669   $170.07   $170.05   $170.10  
  Purchase #4 $24.77   5.615%   $26.1608   $26.16   $26.15   $26.20  
  Purchase #5 $192.62   11.703%   $215.1623   $215.16   $215.15   $215.20  
  Purchase #6 $178.65   12.663%   $201.2724   $201.27   $201.25   $201.30  
  Purchase #7 $7.73   10.852%   $8.5689   $8.57   $8.55   $8.60  
  7 purchase totals = $984.34       $1,068.8283   $1,068.83   $1,068.75   $1,069.00