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 $104.78   9.702%   $114.9458   $114.95   $114.95   $114.90  
  Purchase #2 $170.85   3.426%   $176.7033   $176.70   $176.70   $176.70  
  Purchase #3 $187.44   7.705%   $201.8823   $201.88   $201.90   $201.90  
  Purchase #4 $63.80   6.429%   $67.9017   $67.90   $67.90   $67.90  
  Purchase #5 $184.96   4.656%   $193.5717   $193.57   $193.55   $193.60  
  Purchase #6 $108.46   10.397%   $119.7366   $119.74   $119.75   $119.70  
  Purchase #7 $38.44   9.188%   $41.9719   $41.97   $41.95   $42.00  
  7 purchase totals = $858.73       $916.7133   $916.71   $916.70   $916.70