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 $60.56   10.653%   $67.0115   $67.01   $67.00   $67.00  
  Purchase #2 $104.96   8.663%   $114.0527   $114.05   $114.05   $114.10  
  Purchase #3 $41.86   11.379%   $46.6232   $46.62   $46.60   $46.60  
  Purchase #4 $77.53   4.151%   $80.7483   $80.75   $80.75   $80.70  
  Purchase #5 $187.99   7.236%   $201.593   $201.59   $201.60   $201.60  
  Purchase #6 $196.91   12.712%   $221.9412   $221.94   $221.95   $221.90  
  Purchase #7 $37.26   4.311%   $38.8663   $38.87   $38.85   $38.90  
  7 purchase totals = $707.07       $770.8362   $770.83   $770.80   $770.80