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 $204.91   8.358%   $222.0364   $222.04   $222.05   $222.00  
  Purchase #2 $125.40   4.763%   $131.3728   $131.37   $131.35   $131.40  
  Purchase #3 $13.81   10.659%   $15.282   $15.28   $15.30   $15.30  
  Purchase #4 $50.52   4.332%   $52.7085   $52.71   $52.70   $52.70  
  Purchase #5 $229.62   3.351%   $237.3146   $237.31   $237.30   $237.30  
  Purchase #6 $241.44   8.310%   $261.5037   $261.50   $261.50   $261.50  
  Purchase #7 $107.83   7.409%   $115.8191   $115.82   $115.80   $115.80  
  7 purchase totals = $973.53       $1,036.0371   $1,036.03   $1,036.00   $1,036.00