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 $207.66   3.489%   $214.9053   $214.91   $214.90   $214.90  
  Purchase #2 $8.28   13.588%   $9.4051   $9.41   $9.40   $9.40  
  Purchase #3 $22.56   7.460%   $24.243   $24.24   $24.25   $24.20  
  Purchase #4 $218.56   13.802%   $248.7257   $248.73   $248.75   $248.70  
  Purchase #5 $182.77   5.862%   $193.484   $193.48   $193.50   $193.50  
  Purchase #6 $60.37   13.825%   $68.7162   $68.72   $68.70   $68.70  
  Purchase #7 $163.53   6.332%   $173.8847   $173.88   $173.90   $173.90  
  7 purchase totals = $863.73       $933.3640   $933.37   $933.40   $933.30