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 $241.36   11.827%   $269.9056   $269.91   $269.90   $269.90  
  Purchase #2 $237.85   4.547%   $248.665   $248.67   $248.65   $248.70  
  Purchase #3 $200.80   3.401%   $207.6292   $207.63   $207.65   $207.60  
  Purchase #4 $56.26   12.313%   $63.1873   $63.19   $63.20   $63.20  
  Purchase #5 $204.52   8.693%   $222.2989   $222.30   $222.30   $222.30  
  Purchase #6 $241.59   8.277%   $261.5864   $261.59   $261.60   $261.60  
  Purchase #7 $197.34   4.380%   $205.9835   $205.98   $206.00   $206.00  
  7 purchase totals = $1,379.72       $1,479.2559   $1,479.27   $1,479.30   $1,479.30