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 $219.28   3.479%   $226.9088   $226.91   $226.90   $226.90  
  Purchase #2 $38.92   11.247%   $43.2973   $43.30   $43.30   $43.30  
  Purchase #3 $26.65   13.687%   $30.2976   $30.30   $30.30   $30.30  
  Purchase #4 $16.93   6.639%   $18.054   $18.05   $18.05   $18.10  
  Purchase #5 $229.82   13.677%   $261.2525   $261.25   $261.25   $261.30  
  Purchase #6 $231.85   8.255%   $250.9892   $250.99   $251.00   $251.00  
  Purchase #7 $105.87   12.734%   $119.3515   $119.35   $119.35   $119.40  
  7 purchase totals = $869.32       $950.1509   $950.15   $950.15   $950.30