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 $176.28   8.749%   $191.7027   $191.70   $191.70   $191.70  
  Purchase #2 $6.31   5.627%   $6.6651   $6.67   $6.65   $6.70  
  Purchase #3 $143.81   5.853%   $152.2272   $152.23   $152.25   $152.20  
  Purchase #4 $244.81   5.283%   $257.7433   $257.74   $257.75   $257.70  
  Purchase #5 $233.83   11.335%   $260.3346   $260.33   $260.35   $260.30  
  Purchase #6 $149.41   11.279%   $166.262   $166.26   $166.25   $166.30  
  Purchase #7 $194.83   5.499%   $205.5437   $205.54   $205.55   $205.50  
  7 purchase totals = $1,149.28       $1,240.4786   $1,240.47   $1,240.50   $1,240.40