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 $206.90   9.388%   $226.3238   $226.32   $226.30   $226.30  
  Purchase #2 $230.96   4.471%   $241.2862   $241.29   $241.30   $241.30  
  Purchase #3 $32.91   3.797%   $34.1596   $34.16   $34.15   $34.20  
  Purchase #4 $242.60   7.817%   $261.564   $261.56   $261.55   $261.60  
  Purchase #5 $102.32   7.308%   $109.7975   $109.80   $109.80   $109.80  
  Purchase #6 $30.36   3.577%   $31.446   $31.45   $31.45   $31.40  
  Purchase #7 $82.49   4.552%   $86.2449   $86.24   $86.25   $86.20  
  7 purchase totals = $928.54       $990.8220   $990.82   $990.80   $990.80