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 $105.83   10.166%   $116.5887   $116.59   $116.60   $116.60  
  Purchase #2 $79.29   13.120%   $89.6928   $89.69   $89.70   $89.70  
  Purchase #3 $23.98   13.169%   $27.1379   $27.14   $27.15   $27.10  
  Purchase #4 $237.76   10.838%   $263.5284   $263.53   $263.55   $263.50  
  Purchase #5 $99.29   5.174%   $104.4273   $104.43   $104.45   $104.40  
  Purchase #6 $241.92   4.416%   $252.6032   $252.60   $252.60   $252.60  
  Purchase #7 $199.92   5.630%   $211.1755   $211.18   $211.20   $211.20  
  7 purchase totals = $987.99       $1,065.1538   $1,065.16   $1,065.25   $1,065.10