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 $95.92   8.640%   $104.2075   $104.21   $104.20   $104.20  
  Purchase #2 $76.90   3.712%   $79.7545   $79.75   $79.75   $79.80  
  Purchase #3 $155.80   11.140%   $173.1561   $173.16   $173.15   $173.20  
  Purchase #4 $246.30   6.271%   $261.7455   $261.75   $261.75   $261.70  
  Purchase #5 $200.41   13.786%   $228.0385   $228.04   $228.05   $228.00  
  Purchase #6 $194.82   5.858%   $206.2326   $206.23   $206.25   $206.20  
  Purchase #7 $113.30   3.143%   $116.861   $116.86   $116.85   $116.90  
  7 purchase totals = $1,083.45       $1,169.9957   $1,170.00   $1,170.00   $1,170.00