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 $231.63   4.593%   $242.2688   $242.27   $242.25   $242.30  
  Purchase #2 $166.89   12.621%   $187.9532   $187.95   $187.95   $188.00  
  Purchase #3 $76.80   6.144%   $81.5186   $81.52   $81.50   $81.50  
  Purchase #4 $193.36   3.265%   $199.6732   $199.67   $199.65   $199.70  
  Purchase #5 $227.90   3.175%   $235.1358   $235.14   $235.15   $235.10  
  Purchase #6 $250.66   13.466%   $284.4139   $284.41   $284.40   $284.40  
  Purchase #7 $182.93   12.248%   $205.3353   $205.34   $205.35   $205.30  
  7 purchase totals = $1,330.17       $1,436.2988   $1,436.30   $1,436.25   $1,436.30