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 $192.26   11.172%   $213.7393   $213.74   $213.75   $213.70  
  Purchase #2 $8.80   8.724%   $9.5677   $9.57   $9.55   $9.60  
  Purchase #3 $187.72   10.844%   $208.0764   $208.08   $208.10   $208.10  
  Purchase #4 $70.77   8.266%   $76.6198   $76.62   $76.60   $76.60  
  Purchase #5 $189.68   8.443%   $205.6947   $205.69   $205.70   $205.70  
  Purchase #6 $164.92   3.595%   $170.8489   $170.85   $170.85   $170.80  
  Purchase #7 $76.87   3.167%   $79.3045   $79.30   $79.30   $79.30  
  7 purchase totals = $891.02       $963.8513   $963.85   $963.85   $963.80