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 $11.95   6.377%   $12.7121   $12.71   $12.70   $12.70  
  Purchase #2 $175.70   5.271%   $184.9611   $184.96   $184.95   $185.00  
  Purchase #3 $230.25   5.104%   $242.002   $242.00   $242.00   $242.00  
  Purchase #4 $205.42   4.105%   $213.8525   $213.85   $213.85   $213.90  
  Purchase #5 $22.52   5.413%   $23.739   $23.74   $23.75   $23.70  
  Purchase #6 $81.62   4.499%   $85.2921   $85.29   $85.30   $85.30  
  Purchase #7 $230.42   13.448%   $261.4069   $261.41   $261.40   $261.40  
  7 purchase totals = $957.88       $1,023.9657   $1,023.96   $1,023.95   $1,024.00