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 $208.42   12.571%   $234.6205   $234.62   $234.60   $234.60  
  Purchase #2 $191.26   3.655%   $198.2506   $198.25   $198.25   $198.30  
  Purchase #3 $114.47   5.862%   $121.1802   $121.18   $121.20   $121.20  
  Purchase #4 $92.71   3.831%   $96.2617   $96.26   $96.25   $96.30  
  Purchase #5 $74.80   5.438%   $78.8676   $78.87   $78.85   $78.90  
  Purchase #6 $158.64   3.564%   $164.2939   $164.29   $164.30   $164.30  
  Purchase #7 $53.49   9.801%   $58.7326   $58.73   $58.75   $58.70  
  7 purchase totals = $893.79       $952.2071   $952.20   $952.20   $952.30