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 $235.83   11.232%   $262.3184   $262.32   $262.30   $262.30  
  Purchase #2 $207.62   5.660%   $219.3713   $219.37   $219.35   $219.40  
  Purchase #3 $98.28   6.703%   $104.8677   $104.87   $104.85   $104.90  
  Purchase #4 $242.57   8.191%   $262.4389   $262.44   $262.45   $262.40  
  Purchase #5 $144.62   13.865%   $164.6716   $164.67   $164.65   $164.70  
  Purchase #6 $245.93   4.214%   $256.2935   $256.29   $256.30   $256.30  
  Purchase #7 $158.63   6.154%   $168.3921   $168.39   $168.40   $168.40  
  7 purchase totals = $1,333.48       $1,438.3535   $1,438.35   $1,438.30   $1,438.40