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 $213.71   11.811%   $238.9513   $238.95   $238.95   $239.00  
  Purchase #2 $25.45   11.435%   $28.3602   $28.36   $28.35   $28.40  
  Purchase #3 $226.29   12.205%   $253.9087   $253.91   $253.90   $253.90  
  Purchase #4 $218.34   7.300%   $234.2788   $234.28   $234.30   $234.30  
  Purchase #5 $168.35   3.536%   $174.3029   $174.30   $174.30   $174.30  
  Purchase #6 $16.90   11.551%   $18.8521   $18.85   $18.85   $18.90  
  Purchase #7 $234.85   11.149%   $261.0334   $261.03   $261.05   $261.00  
  7 purchase totals = $1,103.89       $1,209.6874   $1,209.68   $1,209.70   $1,209.80