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 $49.66   13.456%   $56.3422   $56.34   $56.35   $56.30  
  Purchase #2 $199.67   10.743%   $221.1205   $221.12   $221.10   $221.10  
  Purchase #3 $230.72   5.176%   $242.6621   $242.66   $242.65   $242.70  
  Purchase #4 $19.37   12.577%   $21.8062   $21.81   $21.80   $21.80  
  Purchase #5 $186.92   6.335%   $198.7614   $198.76   $198.75   $198.80  
  Purchase #6 $114.71   3.126%   $118.2958   $118.30   $118.30   $118.30  
  Purchase #7 $40.44   12.109%   $45.3369   $45.34   $45.35   $45.30  
  7 purchase totals = $841.49       $904.3251   $904.33   $904.30   $904.30