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 $168.85   7.292%   $181.1625   $181.16   $181.15   $181.20  
  Purchase #2 $120.45   3.231%   $124.3417   $124.34   $124.35   $124.30  
  Purchase #3 $181.63   6.336%   $193.1381   $193.14   $193.15   $193.10  
  Purchase #4 $230.66   13.425%   $261.6261   $261.63   $261.65   $261.60  
  Purchase #5 $67.54   6.143%   $71.689   $71.69   $71.70   $71.70  
  Purchase #6 $229.68   13.161%   $259.9082   $259.91   $259.90   $259.90  
  Purchase #7 $143.51   10.167%   $158.1007   $158.10   $158.10   $158.10  
  7 purchase totals = $1,142.32       $1,249.9663   $1,249.97   $1,250.00   $1,249.90