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 $57.71   10.655%   $63.859   $63.86   $63.85   $63.90  
  Purchase #2 $63.99   5.645%   $67.6022   $67.60   $67.60   $67.60  
  Purchase #3 $175.98   6.333%   $187.1248   $187.12   $187.10   $187.10  
  Purchase #4 $92.53   5.248%   $97.386   $97.39   $97.40   $97.40  
  Purchase #5 $104.36   9.216%   $113.9778   $113.98   $114.00   $114.00  
  Purchase #6 $63.89   3.567%   $66.169   $66.17   $66.15   $66.20  
  Purchase #7 $168.26   6.852%   $179.7892   $179.79   $179.80   $179.80  
  7 purchase totals = $726.72       $775.9080   $775.91   $775.90   $776.00