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 $245.29   6.761%   $261.8741   $261.87   $261.85   $261.90  
  Purchase #2 $25.91   6.711%   $27.6488   $27.65   $27.65   $27.60  
  Purchase #3 $165.50   6.590%   $176.4065   $176.41   $176.40   $176.40  
  Purchase #4 $48.76   9.656%   $53.4683   $53.47   $53.45   $53.50  
  Purchase #5 $208.31   6.196%   $221.2169   $221.22   $221.20   $221.20  
  Purchase #6 $11.32   5.354%   $11.9261   $11.93   $11.95   $11.90  
  Purchase #7 $212.37   10.458%   $234.5797   $234.58   $234.60   $234.60  
  7 purchase totals = $917.46       $987.1204   $987.13   $987.10   $987.10