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 $218.52   8.271%   $236.5938   $236.59   $236.60   $236.60  
  Purchase #2 $87.33   5.870%   $92.4563   $92.46   $92.45   $92.50  
  Purchase #3 $158.46   11.596%   $176.835   $176.84   $176.85   $176.80  
  Purchase #4 $66.86   6.351%   $71.1063   $71.11   $71.10   $71.10  
  Purchase #5 $230.57   13.287%   $261.2058   $261.21   $261.20   $261.20  
  Purchase #6 $134.99   5.673%   $142.648   $142.65   $142.65   $142.60  
  Purchase #7 $191.50   11.851%   $214.1947   $214.19   $214.20   $214.20  
  7 purchase totals = $1,088.23       $1,195.0399   $1,195.05   $1,195.05   $1,195.00