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 $196.40   6.144%   $208.4668   $208.47   $208.45   $208.50  
  Purchase #2 $248.26   10.394%   $274.0641   $274.06   $274.05   $274.10  
  Purchase #3 $151.32   8.755%   $164.5681   $164.57   $164.55   $164.60  
  Purchase #4 $227.45   9.237%   $248.4596   $248.46   $248.45   $248.50  
  Purchase #5 $51.58   7.119%   $55.252   $55.25   $55.25   $55.30  
  Purchase #6 $209.27   8.387%   $226.8215   $226.82   $226.80   $226.80  
  Purchase #7 $25.55   10.837%   $28.3189   $28.32   $28.30   $28.30  
  7 purchase totals = $1,109.83       $1,205.9510   $1,205.95   $1,205.85   $1,206.10