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 $63.34   6.688%   $67.5762   $67.58   $67.60   $67.60  
  Purchase #2 $237.62   9.863%   $261.0565   $261.06   $261.05   $261.10  
  Purchase #3 $176.65   8.550%   $191.7536   $191.75   $191.75   $191.80  
  Purchase #4 $186.77   13.853%   $212.6432   $212.64   $212.65   $212.60  
  Purchase #5 $158.92   4.578%   $166.1954   $166.20   $166.20   $166.20  
  Purchase #6 $203.29   11.223%   $226.1052   $226.11   $226.10   $226.10  
  Purchase #7 $250.94   11.407%   $279.5647   $279.56   $279.55   $279.60  
  7 purchase totals = $1,277.53       $1,404.8948   $1,404.90   $1,404.90   $1,405.00