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 $127.48   13.506%   $144.6974   $144.70   $144.70   $144.70  
  Purchase #2 $187.84   5.418%   $198.0172   $198.02   $198.00   $198.00  
  Purchase #3 $116.87   13.198%   $132.2945   $132.29   $132.30   $132.30  
  Purchase #4 $186.69   13.563%   $212.0108   $212.01   $212.00   $212.00  
  Purchase #5 $51.78   13.606%   $58.8252   $58.83   $58.85   $58.80  
  Purchase #6 $125.62   6.271%   $133.4976   $133.50   $133.50   $133.50  
  Purchase #7 $85.88   5.838%   $90.8937   $90.89   $90.90   $90.90  
  7 purchase totals = $882.16       $970.2364   $970.24   $970.25   $970.20